Polylactic acid fiber non-woven fabric and preparation and application thereof

Abstract

The invention discloses a polylactic acid fiber non-woven fabric preparation method, which comprises: putting PLA particles into a vacuum dryer, drying at 60-80 DEG C for 4-6 h, and feeding the dried PLA particles into a storage hopper of a screw extruder through a screw conveyor; pLA particles are melted and plasticized through an extruder, melt is filtered through a metal sintering filter screen, a gear pump is used for conveying and metering, and the melt is conveyed to a spinning assembly; manufacturing the melt into a polylactic acid fiber net by using a spinning assembly; winding the polylactic acid fiber net by using a winding machine; the temperature of the screw extruder is controlled in a partitioned manner, the screw extruder comprises a feeding section, a compression section and a homogenization section, the temperature of the feeding section is 150-160 DEG C, the temperature of the compression section is 170-180 DEG C, and the temperature of the homogenization section is 180-190 DEG C; in the spinneret plate assembly, spinneret orifices are special-shaped orifices. The method can guarantee the mechanical property of the fiber, improve the interception efficiency of the non-woven fabric and improve the longitudinal tensile strength of the non-woven fabric. The method is more suitable for manufacturing masks, wet tissues, packaging bags, sanitary napkins and paper diapers.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical fiber preparation, and specifically relates to a polylactic acid fiber non-woven fabric and its preparation and uses. Background Art

[0002] The application of traditional petroleum-based non-woven fabrics, such as polypropylene and polyethylene, in disposable hygiene products faces severe challenges. These materials have problems such as non-degradability, microplastic pollution, and high carbon emissions during the production process. According to statistics from the United Nations Environment Programme, approximately 30 million tons of hygiene product waste are generated globally each year, and more than 70% of them are petroleum-based non-woven fabrics, exacerbating soil and ocean pollution. To replace traditional materials, biodegradable polymers such as polylactic acid (PLA) have become a research hotspot. PLA is derived from renewable resources such as corn and sugarcane and can be degraded into CO 2 and water within 180 days through composting, meeting the EU EN13432 standard. However, there are still some problems in the large-scale application of PLA fibers in the hygiene product field:

[0003] In the traditional melt spinning process, the processing temperature window of PLA is narrow, usually 170 - 200 °C, and it is extremely sensitive to temperature fluctuations. Most existing equipment uses a single temperature zone or broad temperature control, such as 180 - 210 °C throughout the process, resulting in local overheating of PLA in the extruder, causing thermal degradation, with the molecular weight reduction rate reaching as high as 10% - 15%, seriously affecting the fiber strength, and the tensile strength is usually less than 10 MPa. At the same time, uneven melt viscosity easily causes spinneret blockage, poor production continuity, and the qualified product rate is less than 85%.

[0004] In the patent with the application number CN202410666169.4, a polylactic acid fiber, a polylactic acid non-woven fabric, and a preparation method are disclosed; by uniformly mixing PLLA and PDLA with a solvent in a certain proportion to obtain a spinning solution, spraying the spinning solution from a flash spinning nozzle to obtain polylactic acid fibers, and uniformly laying and hot-rolling the polylactic acid fibers to obtain a polylactic acid non-woven fabric. The polylactic acid non-woven fabric prepared in this way has the properties of light weight, high strength, waterproof and breathable, biodegradable, and good thermal stability. The non-woven fabric manufactured by this method has high hydrophobicity, resulting in a slow liquid absorption rate and difficulty in meeting the requirements of sanitary napkins and diapers for rapid liquid penetration. Summary of the Invention

[0005] The purpose of the present invention is to provide a polylactic acid fiber non-woven fabric and its preparation and uses to solve the following technical problems raised in the background art:

[0006] The insufficient stability of the processing technology in the prior art leads to insufficient strength of the produced fibers.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is:

[0008] A method for preparing a polylactic acid fiber non-woven fabric includes the following steps:

[0009] A. Put PLA particles into a vacuum dryer and dry them at 60 - 80°C for 4 - 6 hours, and send the dried PLA particles into the hopper of a screw extruder through a screw conveyor;

[0010] B. Melt and plasticize the PLA particles by using an extruder, filter the melt through a metal sintered filter screen, use a gear pump for transmission and metering, and transmit the melt to a spinneret assembly;

[0011] C. Use the spinneret assembly to make the melt into a polylactic acid fiber web;

[0012] D. Wind up the polylactic acid fiber web by using a winder;

[0013] Among them, the temperature of the screw extruder is controlled in zones. The screw extruder includes a feeding section, a compression section, and a homogenizing section. Among them, the feeding section is 150 - 160°C, the compression section is 170 - 180°C, and the homogenizing section is 180 - 190°C;

[0014] In the spinneret plate assembly, the spinneret holes are special-shaped holes.

[0015] Further, in step A, a negative pressure suction feeder is used to send the dried PLA particles into the hopper of the screw extruder.

[0016] Further, the mesh number of the metal sintered filter screen is 200 - 400 meshes, and the pore diameter is 20 - 75μm; differential pressure sensors are arranged on both sides of the metal sintered filter screen.

[0017] Further, in step C, after the spinneret assembly extrudes the melt, the melt stream is drawn by a high-speed hot air flow. The temperature of the hot air flow is 200 - 250°C, the air flow speed is 0.5 - 1.5 Mach, and the angle between the air flow direction and the vertical direction of the spinneret plate is 15° - 30°.

[0018] Further, in step C, after the fiber web is formed, it is cooled and solidified by a cold air system. The cold air temperature is 10 - 25°C, the wind speed is 5 - 10m / s, and the air volume is 200 - 500m / h.

[0019] Further, in step D, the winding tension is 5 - 50N, the winding speed is 10 - 50m / min, and the flatness of the coil is controlled by a surface friction roller or a center winding method.

[0020] Further, after step D, there is also a hot rolling reinforcement process, and the fiber web is hot rolled. The hot rolling temperature is 80 - 100°C, the linear pressure is 50 - 200N / mm, and the roll point density is 20 - 50 points / cm 2 .

[0021] Furthermore, the properties of the prepared polylactic acid fiber non-woven fabric meet the following indicators: the longitudinal tensile strength ≥ 15 MPa, the transverse tensile strength ≥ 10 MPa, the air permeability is 100 - 500 L / m / s, and the filtration efficiency for 0.3 μm particles ≥ 95%.

[0022] Furthermore, the waste generated during the production process is pulverized and recycled into the new material at a ratio of 5% - 10% for recycling, and the particle size after pulverization ≤ 3 mm.

[0023] A use of a polylactic acid fiber non-woven fabric, the polylactic acid fiber non-woven fabric in the previous aspect is used to manufacture masks, wet wipes, packaging bags, sanitary napkins, and diapers.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The screw extruder of the present invention adopts zone temperature control. The low temperature in the feeding section prevents premature softening of the raw material, which may cause bridging and blockage. The temperature is gradually increased in the compression section, and uniform plasticization is achieved through the shearing action of the screw. The homogenization section ensures complete homogenization of the melt and avoids thermal decomposition of PLA. Through this design, the melt viscosity is stabilized at 500 - 800 Pa·s, the residence time is less than or equal to 3 minutes, and the molecular weight reduction rate is less than 5%, thereby ensuring the mechanical properties of the fiber.

[0026] The high temperature in the homogenization section enhances the fluidity of the melt, and cooperates with the metal sintered filter screen to efficiently remove impurities, thereby reducing the risk of spinneret blockage.

[0027] The present invention also adopts a special-shaped hole spinneret. Compared with circular holes, the special-shaped holes can increase the specific surface area and surface roughness of the fiber. More tortuous channels are formed between the fibers, improving the interception efficiency. The bonding force between the cross-section fibers is stronger, and the longitudinal tensile strength of the non-woven fabric is improved.

[0028] The polylactic acid fiber non-woven fabric manufactured by using the method of the present invention is more suitable for manufacturing masks, wet wipes, packaging bags, sanitary napkins, and diapers. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a flowchart of the preparation method for preparing the polylactic acid fiber non-woven fabric of the present invention;

[0030] Figure 2 It is a schematic diagram of the production process of a polylactic acid fiber of the present invention;

[0031] Figure 3 It is a schematic diagram of the production process of a non-woven fabric of the present invention;

[0032] Figure 4 It is a physical electron microscope image of the present invention;

[0033] Figure 5 Schematic diagram of the overall structure of a meltblown die head of the present invention;

[0034] Figure 6 Schematic diagram of the internal structure of a meltblown die head of the present invention;

[0035] Figure 7 Schematic diagram of the internal structure of a spinneret hole of the present invention.

[0036] Markings in the figure: 1 - Substrate, 2 - Intermediate zone, 3 - Intermediate body, 4 - Discharge channel, 5 - Side plate, 6 - Drawing channel, 7 - Spinneret hole, 8 - Spinneret plate, 9 - Air inlet guiding zone, 10 - Air inlet channel, 11 - Air inlet groove, 12 - Air inlet joint, 13 - Heating hole, 14 - Feed channel, 15 - Auxiliary groove. Specific embodiments

[0037] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0038] Embodiment 1:

[0039] This embodiment is used to prepare polylactic acid fiber non-woven fabric. First, the preparation of raw materials is required. In this embodiment, L-type polylactic acid particles are selected as the raw material for preparing polylactic acid fiber non-woven fabric. The L-type polylactic acid particles have specific performance indicators. Its molecular weight is 150,000, and the initial moisture content is 0.08%. The appropriate molecular weight can ensure the fluidity of the melt during subsequent processing and the performance of the final product. Strict control of the moisture content is also an important factor to ensure the product quality.

[0040] Step A: Put the selected L-type polylactic acid particles into a vacuum dryer of model Motan MD-200. Set the temperature of the dryer to 70°C, the vacuum degree to -0.09 MPa, and the drying time to 5 hours. Under such conditions, the moisture in the polylactic acid particles can be effectively removed, and the moisture content after drying successfully drops to 0.03%. Strict control of the moisture content is because the presence of moisture may cause bubbles to generate during the subsequent melting process, affecting the quality and performance of the non-woven fabric.

[0041] After drying is completed, to prevent the particles from absorbing moisture again, the dried PLA particles need to be immediately transported to the hopper of the screw extruder through a closed pipeline and a negative pressure suction feeder. The conveying speed of the negative pressure suction feeder is set at 30 kg / h. This stable conveying speed helps to ensure the continuity and stability of the subsequent production process. At the same time, a level sensor is installed in the hopper, which can monitor the level situation in real time, avoid material shortage or overflow, and thus ensure the smooth progress of production.

[0042] Step B: Start the twin-screw extruder and set it according to specific temperature zones. The temperature of the feeding section is set at 155 °C. This temperature can prevent the particles from softening prematurely, avoid clogging the feeding port, and ensure that the particles can smoothly enter the extruder. The temperature of the compression section is set at 175 °C. At this stage, the screw shears and plasticizes the particles, reducing the melt viscosity to 500 - 800 Pa·s. The appropriate viscosity is beneficial for subsequent extrusion and forming. The temperature of the homogenization section is set at 185 °C, and it is necessary to ensure that the residence time of the melt in this section is ≤ 3 minutes to avoid thermal degradation of polylactic acid and affect the product performance.

[0043] At the same time, set the screw speed at 50 rpm, monitor the torque to ensure that it is ≤ 80%, and keep the melt pressure stable at 10 - 15 MPa. The length-diameter ratio of the extruder screw is 28:1, and the compression ratio is 3.5:1. The setting of these parameters is to achieve effective melting and plasticization of polylactic acid particles.

[0044] The polylactic acid particles form a melt after being extruded by the screw. This melt needs to be filtered through a 300-mesh metal sintered filter screen with a pore diameter of 35 μm. Differential pressure sensors of Wika A-10 model are installed on both sides of the filter screen. When the differential pressure between the two sides of the filter screen > 4 MPa, it means that the filter screen may be blocked by impurities. At this time, an alarm will be triggered and the machine will stop automatically to prevent impurities from entering the subsequent process and affecting the product quality.

[0045] The filtered melt is accurately metered by a gear pump. A Zenith HPD-2 model gear pump is selected. It meters the melt at a flow rate of 2 L / min and can ensure that the outlet pressure fluctuation is ≤ ±0.4%, providing a stable melt supply for the subsequent spinning process.

[0046] Step C: Install the profiled orifice spinneret plate onto the spinning box. Before installation, the spinneret plate needs to be strictly cleaned and dried. The specific operation is to use a 5% NaOH solution and clean it in an ultrasonic cleaner at 40 kHz for 30 minutes to remove impurities and oil stains on the surface of the spinneret plate. After cleaning, use nitrogen for purging and drying to ensure that the surface of the spinneret plate is dry and clean.

[0047] Start the spinneret box heating system, preheat it to 200°C and keep it at this temperature for 20 minutes. The purpose of this is to ensure uniform temperature of the spinneret plate and provide a stable temperature environment for the subsequent spinning process.

[0048] Turn on the annular air knife electric heater and set the hot air flow temperature to 220°C. Adjust the air flow velocity to 1.0 Mach through the Venturi nozzle. At this time, the corresponding pressure is 0.8 MPa, and the air flow direction forms a 20° angle with the vertical direction of the spinneret plate. When the melt is extruded through the spinneret holes, under the stretching action of the high-speed air flow, fibers with a diameter of 5 μm are formed, and the fiber length is between 50 - 100 mm.

[0049] Start the cold air system, set the cold air temperature to 15°C and the wind speed to 8 m / s. Make the cold air evenly distributed through the perforated plate, and ensure that the wind speed deviation ≤ ±5%. The fibers are randomly laid into a web under the action of the negative pressure adsorption device. At the same time, the wire laying device swings horizontally at a frequency of 30 Hz and an amplitude of ±10 cm, and finally a uniform fiber web with a grammage of 50 g / m 2 is formed.

[0050] Step D: Start the winding machine, set the winding tension to 25 N and the winding speed to 30 m / min. Use the surface friction roller to control the flatness of the coil, ensuring that the coil surface is flat and without wrinkles. The initial coil diameter is 150 mm, and the maximum coil diameter is 1000 mm. During coil change, the winding machine will automatically reduce the speed to 5 m / min to ensure that the end face deviation of the coil ≤ 0.8, guaranteeing the appearance quality of the coil.

[0051] Feed the fiber web into the hot rolling machine, set the upper roller temperature to 90°C (using oil heating method), the linear pressure to 100 N / mm, and the roll nip density to 35 points / cm 2 . After hot rolling treatment, the longitudinal tensile strength of the non-woven fabric is increased to 18 MPa, and the transverse tensile strength is increased to 12 MPa, effectively improving the strength and stability of the non-woven fabric.

[0052] Use a slitter to slit the hot-rolled non-woven fabric. The slitter cuts at a speed of 3000 rpm, and the slitting width is set to 1000 mm to cut the non-woven fabric into products that meet the specification requirements.

[0053] Finally, collect the scraps generated during the production process, and process them into particles with a particle size ≤ 2 mm through a crusher. Mix these particles into the new material at a ratio of 8% to achieve the recycling of waste materials, reduce production costs, and also meet the environmental protection requirements.

[0054] Example 2:

[0055] This example is used to test the performance of the polylactic acid fiber non-woven fabric produced in Example 1, including mechanical property testing, filtration efficiency testing, air permeability testing, and biodegradability testing.

[0056] The conditions for mechanical property testing are as follows:

[0057] The equipment is an Instron 5967 universal material testing machine.

[0058] The specimen size is 200×50 mm (length × width)

[0059] The tensile speed is 100 mm / min, which is used to simulate the stress loading rate in actual use.

[0060] The ambient temperature is 23°C.

[0061] The test results are as follows:

[0062] Longitudinal tensile strength: 18 MPa; transverse tensile strength: 12 MPa; elongation at break: 40%.

[0063] Among them, the longitudinal strength is higher than the transverse, indicating that the fiber arrangement in the production direction of the non-woven fabric is denser, which is suitable as a stressed component such as a mask ear strap or a handle of a packaging bag. The 40% elongation rate shows that the material has a certain elasticity and can adapt to dynamic use scenarios such as folding and bending, such as the conformability of sanitary napkins and diapers.

[0064] The conditions for filtration efficiency testing are as follows:

[0065] The equipment is a TSI 8130 automatic filter media tester.

[0066] The aerosol type is 0.3μm NaCl particles, which is the particle size most likely to penetrate the filter media.

[0067] The test flow rate is 85 L / min, which is used to simulate the normal breathing rate of the human body.

[0068] The test results are as follows:

[0069] The filtration efficiency is 97%, and the ventilation resistance is 45 Pa.

[0070] It is concluded that the specific surface area of the polylactic acid fiber produced through the special-shaped holes increases, thus improving the particle interception ability. The high-speed air flow of hot air drawing thins the fiber diameter to 5μm, forming a denser filter layer.

[0071] The conditions for air permeability testing are as follows:

[0072] The equipment is a Textest FX 3300 air permeability tester.

[0073] The test area is 20 cm 2。

[0074] The pressure difference is 100 Pa, which is used to simulate the air flow resistance in daily use.

[0075] The test results are as follows:

[0076] The air permeability is 300 L / m 2 / s.

[0077] It is concluded that under the influence of a hot air flow temperature of 220 °C and an air volume of 300 m / h, the fiber web has a higher fluffiness, resulting in better air permeability.

[0078] The test conditions for the up-and-down degradation are as follows:

[0079] Composting is carried out under the conditions of a temperature of 58 °C ± 2 °C and a humidity of 50%-60%.

[0080] The test results are as follows:

[0081] The degradation rate at 90 days is 85%; the degradation rate at 180 days ≥ 92%.

[0082] It is concluded that the non-woven fabric manufactured by the manufacturing method of the present invention has good degradability and is suitable for the production of disposable products such as degradable packaging bags, sanitary napkins, and diapers, thereby reducing environmental pollution.

[0083] Example 3: Application examples of polylactic acid fiber non-woven fabrics.

[0084] Application 1: Production of medical masks.

[0085] Application 2: Production of environmentally friendly packaging bags.

[0086] Application 3: Production of sanitary napkins.

[0087] Application 4: Production of diapers.

[0088] Example 4:

[0089] This example is used to disclose another preparation method of polylactic acid fiber, which is used to solve the problem that the inherent hydrophobicity of traditional PLA leads to a slow liquid absorption rate and it is difficult to meet the requirements of sanitary napkins and diapers for rapid liquid penetration; at the same time, traditional PLA non-woven fabrics lack additional functions such as antibacterial and breathable properties. As Figure 2 shown, it includes the following steps:

[0090] The PLA particles are added with bamboo fibers after low-temperature melting and high-temperature foaming, and are mixed by a static mixer to form a porous composite melt. The porous composite melt is irradiated with ultraviolet light to form a spinning melt, and the spinning melt is obtained by melt blowing and electrospinning to obtain polylactic acid fibers;

[0091] Among them, the low-temperature melting is controlled at 160 - 170 °C and a composite dispersion liquid is added; the high-temperature foaming is controlled at 175 - 185 °C and supercritical CO and choline ionic liquid are injected;

[0092] The composite dispersion liquid is prepared by high-speed shear emulsification of chitosan nanoparticles, tributyl acetylcitrate, and cellulose nanocrystals. The chitosan nanoparticles are 3 - 5 wt%, tributyl acetylcitrate is 8 - 10 wt%, and cellulose nanocrystals are 0.5 wt%.

[0093] When preparing the spinning melt, the addition amounts of each component are as follows: PLA particles 65 - 70 wt%, bamboo fiber 10 - 15 wt%, supercritical CO 5 - 8 wt%, and choline ionic liquid 1 - 3 wt%.

[0094] In a preferred embodiment, the preparation method of the PLA particles includes copolymerizing L-lactide and D-lactide, and grafting polyethylene glycol onto the PLA molecular chain through reactive extrusion.

[0095] Among them, the catalyst is stannous octoate, L-lactide is 92 - 95 wt%, D-lactide is 5 - 8 wt%, and polyethylene glycol is 3 - 5 wt%.

[0096] In a preferred embodiment, 1 - 2 wt% of tea tree oil / mint oil microcapsules are added after the PLA particles are subjected to high-temperature foaming.

[0097] In a preferred embodiment, itaconic anhydride is added during ultraviolet light irradiation, and the addition amount of itaconic anhydride is 0.5 wt%.

[0098] In a preferred embodiment, the spinning melt is melt-sprayed with outer-layer fibers through a melt-blown die head, a high-temperature melt pump, and a compressed air system; the spinning melt generates inner-layer fibers through a high-voltage electrostatic generator, a metering pump, and a metal receiving roll, and the inner-layer fibers and the outer-layer fibers are combined by hot roll pressing.

[0099] A method for preparing a poly(lactic acid) fiber non-woven fabric, as Figure 3 shown, wherein the poly(lactic acid) fiber is prepared by the preparation method described in the previous aspect, and includes the following steps:

[0100] A, Stack the poly(lactic acid) fibers through a conveyor belt;

[0101] B, Form a non-woven fabric through hot air pre-bonding and reinforcement; the temperature is 80 - 85 °C, the wind speed is 2 - 3 m / s, and the time is 10 - 15 s;

[0102] B, Use a high-pressure hydroentangling machine to reinforce the non-woven fabric; the water pressure is 60 - 80 bar, and the water needle density is 40 - 60 holes / cm 2 .

[0103] C, impregnating the non-woven fabric and drying; the impregnation liquid is an aqueous solution of sodium alginate, nanosilver and polyurethane acrylate, the impregnation time is 5-10s, the liquid squeeze rate is 80%, and the hot air is dried at 100°C;

[0104] D, the nonwoven fabric is subjected to plasma treatment; the argon flow rate is 10 L / min, and the treatment speed is 10 m / min;

[0105] E, cutting non-woven fabric.

[0106] In a preferred embodiment, in step A, the CV value of the fiber web uniformity is less than 5%, and the inter-layer alignment deviation is less than 2 mm.

[0107] In a preferred embodiment, in step B, 0.1% citric acid is added to the circulating water of the high-pressure water-jet slingshot to adjust the pH to 5-6.

[0108] A polylactic acid fiber nonwoven fabric is prepared by the preparation method of the polylactic acid fiber nonwoven fabric in the previous aspect.

[0109] A use of a polylactic acid fiber nonwoven fabric, using the nonwoven fabric in the first aspect to manufacture sanitary napkins and diapers.

[0110] Embodiment 5:

[0111] 93 wt% of L-lactide and 7 wt% of D-lactide were added to a reactor, and stannous octoate was used as a catalyst to carry out copolymerization reaction at 180°C and 1 MPa for 2 hours. After the reaction was completed, 4 wt% of polyethylene glycol was added, and reaction extrusion was carried out at 190°C through a reaction extruder to obtain modified PLA particles.

[0112] 4 wt % chitosan nanoparticles, 9 wt % acetyl tributyl citrate and 0.5 wt % cellulose nanocrystals were added to an appropriate amount of deionized water, and sheared and emulsified at a speed of 10000 r / min for 30 minutes in a high-speed shear emulsifier to prepare a composite dispersion.

[0113] PLA pellets were put into a twin-screw extruder, the temperature was controlled at 165°C, and the composite dispersion was added and mixed thoroughly.

[0114] The low-temperature melted PLA melt is transported to a foaming device, heated to 180° C., and injected with 6 wt % supercritical CO and 2 wt % choline ionic liquid for high-temperature foaming.

[0115] Adding bamboo fiber and microcapsules: 12 wt% of bamboo fiber and 1.5 wt% of tea tree oil / peppermint oil microcapsules were added to the foamed PLA melt, and the mixture was fully mixed by a static mixer to form a porous composite melt.

[0116] Transfer the porous composite melt into an ultraviolet irradiation chamber, add 0.5 wt% of itaconic anhydride, and react for 10 minutes under ultraviolet irradiation to form a spinning melt.

[0117] The spinning melt passes through a meltblown die head and an electrospinning device to prepare outer-layer fibers and inner-layer fibers respectively, and then the two layers of fibers are bonded together by hot roll pressing to obtain polylactic acid fibers.

[0118] As Figure 4 shown, Figure 3 The figure shows the electron micrograph of the polylactic acid fiber of the present invention. It can be seen from the picture that the fibers are intertwined with each other, forming abundant pores, which endows the fibers with a large specific surface area, facilitating rapid adsorption and dissipation of liquids, demonstrating good moisture absorption and breathability, and can be used in sanitary products to keep them dry. The fibers are slender and have a certain degree of curvature, indicating good flexibility, which is convenient for processing into various fabrics or non-woven fabric products, and is also conducive to conforming to the human body curve in applications such as sanitary products to enhance the comfort. There are interlaced and entangled situations among the fibers, which can enhance the overall structural stability of the material. After being made into non-woven fabrics or other products, it can withstand a certain amount of external force, is not easy to loosen and break, and ensures the durability of the product.

[0119] Example 6:

[0120] Add 92 wt% of L-lactide and 8 wt% of D-lactide into a reaction kettle, use stannous octoate as a catalyst, and carry out a copolymerization reaction for 3 hours under the conditions of 175 °C and 0.8 MPa. After the reaction is completed, add 3 wt% of polyethylene glycol, and carry out a reactive extrusion operation at 185 °C by means of a reactive extruder to obtain modified PLA particles.

[0121] Add 3 wt% of chitosan nanoparticles, 10 wt% of tributyl acetylcitrate, and 0.5 wt% of cellulose nanocrystals into an appropriate amount of deionized water, and use a high-speed shear emulsifier to carry out shear emulsification at a rotation speed of 11000 r / min for 40 minutes to prepare a composite dispersion.

[0122] Put the PLA particles into a single-screw extruder, control the temperature at 160 °C, and at the same time add the composite dispersion and mix well.

[0123] Transfer the low-temperature molten PLA melt to a foaming device, heat it up to 175 °C, and inject 5 wt% of supercritical CO₂ and 1 wt% of choline ionic liquid for foaming.

[0124] Add 10 wt% of bamboo fibers and 1 wt% of tea tree oil / peppermint oil microcapsules to the foamed melt, and mix well through a static mixer.

[0125] Transfer the mixed melt to an ultraviolet irradiation device, add 0.5 wt% of itaconic anhydride, and irradiate for 12 minutes to form a spinning melt.

[0126] Adopt a combination of meltblowing and electrospinning. First, form the outer layer fibers through a meltblowing die head, then use electrospinning to form the inner layer fibers, and finally obtain polylactic acid fibers through hot roll pressing and compounding.

[0127] Example 7:

[0128] Add 95 wt% of L-lactide and 5 wt% of D-lactide into a reaction kettle, use stannous octoate as a catalyst, and carry out a copolymerization reaction for 1.5 hours under the conditions of 185 °C and 1.2 MPa. After the reaction is completed, add 5 wt% of polyethylene glycol and prepare modified PLA particles through a reactive extrusion mechanism at 200 °C.

[0129] Add 5 wt% of chitosan nanoparticles, 8 wt% of tributyl acetyl citrate, and 0.5 wt% of cellulose nanocrystals into an appropriate amount of deionized water, and shear and emulsify with a high-speed shear emulsifier at a rotation speed of 9000 r / min for 25 minutes to obtain a composite dispersion liquid.

[0130] Add the PLA particles into a twin-screw extruder, control the temperature at 170 °C, and at the same time add the composite dispersion liquid and stir well.

[0131] Transfer the melt after low-temperature melting to a foaming device, heat it up to 185 °C, and inject 8 wt% of supercritical CO₂ and 3 wt% of choline ionic liquid for high-temperature foaming.

[0132] Add 15 wt% of bamboo fibers and 2 wt% of tea tree oil / peppermint oil microcapsules into the foamed melt, and mix well with a static mixer to form a porous composite melt.

[0133] Transfer the porous composite melt to an ultraviolet irradiation area, add 0.5 wt% of itaconic anhydride, and irradiate for 8 minutes to make a spinning melt.

[0134] Prepare the inner and outer layer fibers by meltblowing and electrospinning respectively, and then obtain polylactic acid fibers through hot roll pressing and compounding.

[0135] Example 8:

[0136] Stack the polylactic acid fibers prepared in Example 6 through a conveyor belt, and strictly control the CV value of the web uniformity to be 3% and the layer alignment deviation to be 1 mm.

[0137] Send the stacked web into a hot air pre-bonding device, and process it for 15 s under the conditions of 80 °C and a wind speed of 2 m / s to make the fibers preliminarily bond.

[0138] Reinforce the pre-bonded non-woven fabric using a high-pressure hydroentangling machine, set the water pressure to 60 bar, and the water needle density to 40 holes / cm 2 , and at the same time add 0.1% citric acid to the circulating water to adjust the pH to 5.

[0139] Immerse the reinforced non-woven fabric in an aqueous solution containing sodium alginate, nano-silver, and polyurethane acrylate for 5 s, control the liquor pickup rate at 80%, and then dry it under hot air at 100 °C.

[0140] Perform plasma treatment on the dried non-woven fabric, set the argon gas flow rate to 10 L / min, and the treatment speed to 10 m / min.

[0141] Cut the treated non-woven fabric according to the predetermined size to obtain the polylactic acid fiber non-woven fabric.

[0142] Example 9:

[0143] Use the polylactic acid fibers prepared in Example 7 and stack them through a conveyor belt to ensure that the CV value of the web evenness is 4.5% and the alignment deviation between layers is 1.8 mm.

[0144] Put the stacked web into a hot air pre-bonding device and process it for 10 s under the conditions of 85 °C and a wind speed of 3 m / s to achieve preliminary bonding of the fibers.

[0145] Use a high-pressure hydroentangling machine to further reinforce the pre-bonded non-woven fabric, adjust the water pressure to 80 bar, and the water needle density to 60 holes / cm 2 , and add 0.1% citric acid to the circulating water to make the pH reach 6.

[0146] Immerse the reinforced non-woven fabric in the impregnating solution for 10 s, with a liquor pickup rate of 80%, and then dry it under hot air at 100 °C.

[0147] Perform plasma treatment on the dried non-woven fabric, with an argon gas flow rate of 10 L / min and a treatment speed of 10 m / min.

[0148] Cut the treated non-woven fabric into the required specifications to obtain the polylactic acid fiber non-woven fabric product.

[0149] Example 10:

[0150] Use the polylactic acid fiber non-woven fabric manufactured in Example 8 to manufacture sanitary napkins and diapers.

[0151] Example 11:

[0152] Use the polylactic acid fiber non-woven fabric manufactured in Example 9 to manufacture sanitary napkins and diapers.

[0153] Comparative Example 1:

[0154] The polylactic acid non-woven fabric was prepared by the method of Example 1, except that bamboo fibers were not added.

[0155] The moisture absorption and air permeability of the non-woven fabric prepared in this comparative example decreased significantly. After testing, the air permeability decreased by about 20%, and the moisture absorption rate decreased by about 15%. At the same time, due to the lack of natural antibacterial components in bamboo fibers, the antibacterial performance was also weakened, and the antibacterial rates against Escherichia coli and Staphylococcus aureus decreased by about 10%.

[0156] Comparative Example 2:

[0157] The polylactic acid non-woven fabric was prepared by the method of Example 4, except that ultraviolet light irradiation and itaconic anhydride were not added.

[0158] The strength of the non-woven fabric prepared in this comparative example decreased significantly, and the breaking strength decreased by about 25%. This is because the cross-linking reaction induced by ultraviolet light irradiation and itaconic anhydride was not carried out, and the binding force between fiber molecular chains was weak, resulting in the non-woven fabric being easily broken when stressed.

[0159] Comparative Example 3:

[0160] The polylactic acid non-woven fabric was prepared by the method of Example 4, except that the composite dispersion liquid was not added.

[0161] The softness and processability of the non-woven fabric prepared in this comparative example became worse. Due to the lack of tributyl acetylcitrate, a plasticizer in the composite dispersion liquid, the flexibility of the fibers decreased and the hand feeling was hard. At the same time, the lack of chitosan nanoparticles and cellulose nanocrystals also led to a decrease in the antibacterial and mechanical properties of the non-woven fabric, with the antibacterial rate decreasing by about 8% and the elongation at break decreasing by about 18%.

[0162] Comparative Example 4:

[0163] The polylactic acid non-woven fabric was prepared by the method of Example 4, except that the traditional spinning method was used.

[0164] The non-woven fabric prepared in the comparative example had larger fiber diameters and poorer uniformity, and a smaller specific surface area. This led to a significant decrease in the moisture absorption speed and air permeability of the non-woven fabric, with the moisture absorption speed decreasing by about 30% and the air permeability decreasing by about 25%. At the same time, due to the less refined fiber structure, the loading effects of antibacterial agents and functional microcapsules were also poor, and the antibacterial performance and the persistence of special functions were weakened.

[0165] Table 1 shows the performance test data of Example 4 and Comparative Examples 1-4.

[0166] Table 1

[0167]

[0168] From the comparison between Example 4 and Comparative Example 1, the addition of bamboo fiber has a significant enhancing effect on the moisture absorption and air permeability and antibacterial properties of the non-woven fabric. When bamboo fiber is not added, both the air permeability rate and the moisture absorption rate decrease significantly, and the antibacterial rate also decreases accordingly. This indicates that due to its good air permeability, moisture absorption, and natural antibacterial properties, bamboo fiber can effectively enhance the performance of the polylactic acid fiber non-woven fabric in these aspects, making it more suitable for application in the field of sanitary products.

[0169] From the comparison between Example 4 and Comparative Example 2, ultraviolet light irradiation and the addition of itaconic anhydride can significantly improve the breaking strength of the non-woven fabric. Without this step, the binding force between fiber molecular chains becomes weak, resulting in a significant decrease in the strength of the non-woven fabric, indicating that the cross-linking reaction triggered by this step plays a key role in enhancing the internal structural stability of the fiber and improving the overall strength of the material, which is crucial for ensuring the durability of the product in actual use.

[0170] From the comparison between Example 4 and Comparative Example 3, the components in the composite dispersion play a synergistic role. They can not only improve the fiber flexibility and softness through the plasticizer in it, but also enhance the antibacterial and mechanical properties by relying on chitosan nanoparticles and cellulose nanocrystals. The lack of the composite dispersion will make the non-woven fabric have obvious disadvantages in terms of softness, antibacterial properties, and elongation at break, affecting the comprehensive quality of the product.

[0171] From the comparison between Example 4 and Comparative Example 4, the method of combining melt blowing and electrospinning has obvious advantages compared with the traditional spinning method. The non-woven fabric obtained by the traditional spinning method has larger and less uniform fiber diameters, resulting in a small specific surface area, which in turn leads to a significant reduction in the moisture absorption speed and air permeability performance. At the same time, the antibacterial performance and the persistence of special functions are also affected, indicating that the innovative spinning process helps to improve the fineness and structural advantages of the fiber and better exert the various properties of the material.

[0172] Generally speaking, the data comparison in the table fully proves that in the preparation process of polylactic acid fiber and its non-woven fabric, every step from the selection of raw material components to the key process links has an indispensable impact on the performance of the final product. Only when each link cooperates and acts synergistically can the prepared polylactic acid fiber non-woven fabric possess comprehensive advantages such as environmental protection and degradability, good moisture absorption and air permeability, excellent antibacterial properties, and softness and comfort, meeting the high-quality requirements of materials for sanitary products such as sanitary napkins and diapers.

[0173] Example 12:

[0174] This example discloses a melt blowing die head, which is used in the spinning stage of Examples 4 - 7;

[0175] As Figures 5 to 7As shown in the figure, the meltblown die head includes a base body 1, an intermediate body 3, a spinneret plate 8, and side plates 5. Among them, the base body 1 is connected to the intermediate body 3. The spinneret plate 8 is fixedly connected to the middle position at the bottom of the intermediate body 3. The side plates 5 are fixedly connected to both sides of the bottom of the intermediate body 3 and form a stretching channel 6 with the spinneret plate 8.

[0176] A feed channel 14 is arranged in the middle of the base body 1, an intermediate zone 2 is arranged in the middle of the intermediate body 3, the intermediate zone 2 is communicated with the feed channel 14, a discharge channel 4 is arranged in the middle of the spinneret plate 8, the discharge channel 4 is communicated with the intermediate zone 2, and a plurality of spinneret holes 7 are arranged at the bottom of the spinneret plate 8 located in the discharge channel 4. An air inlet channel 10 is arranged in the side plate 5, air inlet grooves 11 are arranged on both sides of the intermediate body 3, the air inlet channel 10 is communicated with the air inlet grooves 11, the air inlet grooves 11 are communicated with the stretching channel 6, and an air inlet joint 12 is further connected to the side plate 5, and the air inlet joint 12 is communicated with the air inlet channel 10.

[0177] An air inlet guiding zone 9 with a triangular cross-section is arranged between the air inlet groove 11 and the stretching channel 6. The included angle between the air inlet channel 10 and the axial direction of the spinneret hole 7 is 25 - 35 degrees, preferably 30 degrees. As Figure 7 shown, a plurality of auxiliary grooves 15 are arranged on the inner wall of the spinneret hole 7, the auxiliary grooves 15 are evenly spaced in the circumferential direction, and the auxiliary grooves 15 are of a spiral structure.

[0178] Among them, the feed channel 14 arranged in the middle of the base body 1 is used to introduce the polylactic acid melt. The intermediate zone 2 arranged in the middle of the intermediate body 3 is communicated with the feed channel 14, which plays a role in buffering and distributing the melt, so that the melt can flow evenly to the spinneret plate 8. After the melt passes through the feed channel 14, the intermediate zone 2 and the discharge channel 4, it is extruded from the spinneret holes 7 to form fibers. The high-temperature and high-speed air flow enters the air inlet channel 10 through the air inlet joint 12, and then enters the stretching channel 6 through the air inlet grooves 11 to stretch the melt extruded from the spinneret holes 7. This air inlet guiding zone 9 can make the air flow enter the stretching channel 6 more smoothly, and plays a certain role in converging and accelerating the air flow, improving the stretching effect of the air flow on the melt. The included angle between the air inlet channel 10 and the axial direction of the spinneret hole 7 is 25 - 35 degrees, preferably 30 degrees. This angle design can make the air flow act on the melt extruded from the spinneret holes 7 at an appropriate angle, while ensuring the stretching effect, avoiding the excessive impact of the air flow on the melt resulting in fiber breakage or unevenness. The auxiliary grooves 15 arranged in the spinneret holes 7 can increase the friction between the melt and the inner wall of the spinneret holes 7, make the melt form a certain rotation and disturbance during the extrusion process, contribute to improving the fluidity of the melt, and improving the uniformity of the fibers.

[0179] Further optimized, in order to ensure the temperature stability of the polylactic acid melt during the entire flow process, heating holes 13 are arranged on both sides of the intermediate body 3, and electric heating rods are inserted into the heating holes 13.

[0180] A pressure sensor is provided inside the feed channel 14 to monitor the pressure changes of the melt and the air flow in real time. The pressure sensor is connected to the control system, and when the pressure is abnormal, the control system can automatically adjust the feed rate.

[0181] Through the optimized design of the air flow channel and the structure of the spinneret hole 7, the fineness uniformity and tensile properties of the polylactic acid fiber can be effectively improved, making the produced fiber finer and more uniform, thereby enhancing the application effect of the polylactic acid fiber in sanitary products, such as enhancing the softness and moisture absorption of sanitary napkins and diapers.

[0182] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by terms such as "coaxial", "bottom", "one end", "top", "middle", "the other end", "upper", "one side", "top", "inner", "front", "center", "both ends", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, so it cannot be understood as a limitation to the present invention.

[0183] In the present invention, unless otherwise clearly specified and defined, terms such as "installation", "setting", "connection", "fixation", "swivel connection", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. It can be the communication inside two elements or the interaction relationship between two elements. Unless otherwise clearly defined, for those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0184] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a polylactic acid fiber nonwoven fabric, characterized in that: The following steps are involved: A. Put the PLA pellets into a vacuum dryer and dry them at 60-80℃ for 4-6 hours. Then, use a screw conveyor to deliver the dried PLA pellets into the storage hopper of the screw extruder. B, using an extruder to melt and plasticize the PLA particles, filtering the melt through a metal sintered filter screen, and using a gear pump to transfer and meter the melt to a spinneret assembly; C, using a spinneret assembly to manufacture the melt into a polylactic acid fiber web; D. Winding up the polylactic acid fiber web using a winder; The screw extruder has zone temperature control, and the screw extruder includes a feeding section, a compression section, and a homogenizing section. The feeding section is 150-160°C, the compression section is 170-180°C, and the homogenizing section is 180-190°C. In the spinneret assembly, the spinneret holes are special-shaped holes.

2. The method for preparing a polylactic acid fiber nonwoven fabric according to claim 1, characterized in that: In step A, a negative pressure suction machine is used to feed the dried PLA particles into the storage hopper of the screw extruder.

3. The method for preparing a polylactic acid fiber nonwoven fabric according to claim 1, characterized in that: The mesh number of the metal sintered filter is 200-400 meshes, and the pore size is 20-75 μm; differential pressure sensors are arranged on both sides of the metal sintered filter.

4. The method for preparing a polylactic acid fiber nonwoven fabric according to claim 1, characterized in that: In step C, after the spinneret assembly extrude the melt, the melt stream is stretched by a high-speed hot air flow, the hot air flow temperature is 200-250°C, the air flow velocity is 0.5-1.5 Mach, and the air flow direction is at an angle of 15°-30° to the vertical direction of the spinneret.

5. The method for preparing a polylactic acid fiber nonwoven fabric according to claim 1, characterized in that: In step C, after the fiber web is formed, it is cooled and solidified by a cold air system, and the cold air temperature is 10-25° C., the wind speed is 5-10 m / s, and the air volume is 200-500 m / h.

6. The method for preparing a polylactic acid fiber nonwoven fabric according to claim 1, characterized in that: In step D, the winding tension is 5-50N, the winding speed is 10-50m / min, and the flatness of the coil is controlled by a surface friction roller or a center winding method.

7. The method for preparing a polylactic acid fiber nonwoven fabric according to claim 1, characterized in that: Step D also includes a hot rolling reinforcement process, in which the fiber mesh is hot rolled at a temperature of 80-100° C., a line pressure of 50-200 N / mm, and a rolling point density of 20-50 points / cm 2 .

8. The method for preparing a polylactic acid fiber nonwoven fabric according to claim 1, characterized in that: The prepared polylactic acid fiber nonwoven fabric has the following performance indicators: longitudinal tensile strength ≥15MPa, transverse tensile strength ≥10MPa, air permeability 100-500L / m / s, and filtration efficiency for 0.3μm particles ≥95%.

9. The method for preparing a polylactic acid fiber nonwoven fabric according to claim 1, characterized in that: The waste materials generated during the production process are crushed and mixed back into new materials at a ratio of 5%-10% for recycling. The particle size after crushing is ≤3mm.

10. A use of a polylactic acid fiber nonwoven fabric, characterized in that: The polylactic acid fiber nonwoven fabric described in any one of claims 1 to 9 is used to manufacture masks, wet wipes, packaging bags, sanitary napkins, and diapers.

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