Melt-blown spinning process method of bio-based degradable melt-blown non-woven fabric

Abstract

The invention provides a melt-blown spinning process method of a bio-based degradable melt-blown non-woven fabric, and belongs to the technical field of non-woven fabric manufacturing. According to the method, high-melt-index pure polylactic acid is used as a raw material, a superfine fiber net is formed through segmented drying, five-zone temperature control melt extrusion and two-stage airflow drafting and cooling, the charge stability is enhanced by adopting a triple electret process, and finally, the product softness is improved through humidification and thermal refining treatment. According to the invention, the use of chemical additives is completely avoided, the fiber diameter of the product reaches 1-5 [mu] m, the filtering efficiency is greater than or equal to 99%, the airflow resistance is less than or equal to 80 Pa, the degradation rate under a composting condition within 90 days is greater than or equal to 90%, and the technical bottlenecks of poor processability, low filtering efficiency, dependence on additives and the like of the existing degradable melt-blown cloth are solved. The method is suitable for producing environment-friendly non-woven products such as medical masks and filtering materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of non-woven fabric manufacturing, and specifically relates to a melt-blown spinning process method for bio-based degradable melt-blown non-woven fabric, and in particular to an efficient melt-blown process and a multi-electret treatment system based on pure polylactic acid resin, which is suitable for producing melt-blown non-woven materials with excellent filtration performance and biodegradability. Background Art

[0002] Meltblown nonwovens, thanks to their dense mesh structure formed by ultrafine fibers with a diameter of 1-5 μm, possess excellent filtration, shielding, and adsorption properties. They are widely used in medical protection, air purification, and hygiene products. Traditional meltblown fabrics are primarily made from polypropylene (PP), but PP is non-biodegradable and creates permanent environmental pollution upon disposal. It is estimated that over 150 billion masks are discarded worldwide each year, and these masks take hundreds of years to degrade in the natural environment.

[0003] Polylactic acid (PLA), a biodegradable material, is extracted from plant resources such as corn and cassava and can be produced through chemical synthesis. Its final degradation products are CO2 and H2O, making it an ideal environmentally friendly alternative material. 1 However, PLA faces the following technical bottlenecks in meltblown applications:

[0004] Poor Processing Performance: Commercially available PLA generally has a melt index below 100g / 10min, far below the high flowability requirement of 150g / 10min or higher for meltblowing. Existing technologies often enhance flowability by adding flow modifiers such as potassium sorbate and stearate, or by blending with PBAT, PBS, or other polyesters. However, these additives can remain in the product, affecting biodegradability and safety.

[0005] Difficulty in fiber formation: PLA has a slow crystallization rate and low melt strength, making it prone to breakage during high-speed hot air drawing. This results in uneven fiber diameters, generally exceeding 5μm. Existing solutions, such as adding nano-SiO2 or lignin nucleating agents, can accelerate crystallization, but they also pose problems such as particle agglomeration and spinneret clogging.

[0006] Poor electret stability: The filtration efficiency of meltblown fabrics relies on the electrostatic adsorption effect generated by the electret. PLA molecules have weak polarity and a charge storage capacity that is only one-third that of PP, resulting in low filtration efficiency for existing PLA meltblown fabrics. CN104711764B discloses a high-strength, long-lasting electret microfiber PLA meltblown nonwoven material and its preparation method. This material uses nanoparticle additives to improve the electret effect, but also adds non-degradable components.

[0007] Product odor and brittleness: When processed at high temperatures, PLA is prone to racemization reactions to produce lactic acid oligomers, resulting in a sour odor and a hard and brittle feel to the product.

[0008] In response to the above problems, existing patented technologies have obvious deficiencies:

[0009] CN112694730A discloses a method for preparing high-performance and high-fluidity polylactic acid based on hyperbranched polymers. Hyperbranched polymers are used to improve the fluidity of PLA, but high-temperature mixing is required, which results in high energy consumption.

[0010] CN119372909A discloses an ultra-high melt index polylactic acid resin and its preparation method and application, which utilizes a modified lignin nucleating agent to accelerate PLA crystallization, but involves complex acylation reactions and nanoprecipitation processes.

[0011] LU500385B1 published a method for preparing biodegradable filter materials, which improves the electrostatic potential of filter materials through high-energy electron beam treatment. However, this method does not address the fundamental problem of the weak charge storage capacity of PLA molecules themselves.

[0012] CN113403750B discloses a fully degradable non-woven fabric produced by the meltblowing method and its application in medical masks. Although it achieves fully degradable meltblown fabric, it relies on material modification and the process details are not disclosed. Summary of the Invention

[0013] The core problem solved by the present invention is to overcome the limitation of existing bio-based degradable meltblown fabric production that must rely on chemical additives to improve processing performance; improve the fiber uniformity, filtration efficiency and charge stability of pure PLA meltblown fabric; simplify the process flow and reduce costs.

[0014] To achieve the above object, the present invention provides the following technical solution: a melt-blown spinning process for a bio-based degradable melt-blown non-woven fabric, comprising the following steps:

[0015] S1 using a melt index of 150-300g / 10min pure polylactic acid resin ie PLA resin as raw material;

[0016] S2. The PLA resin is dried at 60-80 ° C for 4-8 hours to a water content of ≤50ppm;

[0017] S3. The dried PLA resin is added to the melt-blown equipment and melt-extruded at a temperature range of 170-220 ° C;

[0018] S4. The melt is extruded through a spinneret with an aperture of 0.2-0.4 mm, and the melt stream is stretched using high-speed hot air at 230-280°C. The hot air pressure is 0.2-0.5 MPa and the flow rate is 2000-3000 m 3 / h;

[0019] S5. A low-temperature airflow cooling zone is provided below the spinneret, the cooling airflow temperature is 10-25°C, and the wind speed is 5-15m / s;

[0020] S6. The drawn microfibers are collected on a receiving device 150-300mm away from the spinneret to form a fiber web;

[0021] S7. The fiber web is subjected to multiple electret treatments, including low-temperature plasma pretreatment, high-voltage electrostatic electret treatment, and charge enhancement treatment;

[0022] S8. The electret treated fiber web is subjected to humidification and tempering treatment, and the ambient humidity is controlled at 40-70% and the temperature is 20-35 ℃;

[0023] S9. Rewind to obtain the finished bio-based degradable meltblown non-woven fabric.

[0024] Preferably, the multi-electret treatment specifically includes:

[0025] S71 low-temperature plasma pretreatment: using argon / oxygen gas mixture, power 500-2000W, frequency 10-40kHz treatment conditions for 0.5-3 seconds;

[0026] S72. High-voltage electrostatic charging: corona discharge treatment at a voltage of 30-100 kV and an electrode distance of 50-200 mm;

[0027] S73. Charge enhancement treatment: Electron beam irradiation is used with an irradiation dose of 5-30 kGy.

[0028] Preferably, the meltblowing equipment includes a twin-screw extruder with five temperature control intervals: zone one 170-180°C, zone two 180-190°C, zone three 190-200°C, zone four 200-210°C, and die head zone 210-220°C.

[0029] Preferably, the cooling air flow is dehumidified air with a relative humidity of ≤30%, and the cooling zone is 10-50 mm away from the spinneret outlet.

[0030] Preferably, the receiving device is a rotary drum web forming machine with negative pressure adsorption, the negative pressure value is 500-2000 Pa, and the linear speed of the rotary drum surface is 5-30 m / min.

[0031] Preferably, an ultrasonic humidification system is used in the humidification and conditioning treatment, the water mist particle size is 5-20 μm, and the treatment time is 10-60 minutes.

[0032] Preferably, the polylactic acid resin is a stereocomplex composed of left-handed polylactic acid PLLA and right-handed polylactic acid PDLA in a ratio of 90:10-70:30.

[0033] Preferably, the molecular structure of the stereocomplex is designed as follows:

[0034] PLLA: It is polymerized from L-lactic acid monomers to form a left-handed helical conformation;

[0035] PDLA: It is formed by the polymerization of D-lactic acid monomers to form a right-handed helical conformation;

[0036] After the two are melt-blended in a ratio of 90:10 to 70:30, a staggered three-dimensional network structure is formed through stereo-complex crystallization. Its crystallization temperature is 40-50°C higher than that of a single component, and the melting point is 210-230°C.

[0037] Preferably, the method for preparing the stereocomplex is:

[0038] S11. Material pretreatment: PLLA and PDLA are vacuum dried separately at 80°C for 6 hours with a moisture content of ≤100 ppm; melt blended in a twin-screw extruder at a target ratio at a temperature of 180-200°C, a rotation speed of 200-300 rpm, and a residence time of 2-5 minutes; and 0.01-0.1 wt% of a hindered phenolic antioxidant is added during melt blending.

[0039] S12. Stereocomplex Dynamic Control:

[0040] After blending, the temperature is rapidly cooled to below 100°C to inhibit homocrystallization; and annealed at 120-140°C for 10-30 minutes to promote the growth of SC crystal nuclei, with a grain size of 50-200 nm.

[0041] Preferably, the weight average molecular weight ratio of PLLA to PDLA is 1:1-1:1.5, and the molecular weight distribution index is ≤1.8.

[0042] The biodegradable melt-blown nonwoven fabric prepared by the present invention has a fiber diameter of 1-5 μm and a gram weight of 10-100 g / m 2 , filtration efficiency for 0.3μm particles ≥99%, air flow resistance ≤80Pa, breaking strength ≥2.5N / cm.

[0043] The biodegradable melt-blown non-woven fabric prepared by the invention has a biodegradation rate of ≥90% within 90 days under standard composting conditions of 58° C.±2° C. and 60-80% humidity.

[0044] The bio-based degradable melt-blown non-woven fabric prepared by the present invention is used in medical masks, air filter materials, liquid filter materials or sanitary products.

[0045] This invention proposes a melt-blown spinning method based on pure PLA resin and a multi-electret synergistic process. Without any chemical additives, the method optimizes process parameters and introduces an innovative electret system to achieve the production of high-performance, fully biodegradable melt-blown fabrics. Key innovations include:

[0046] 1. Selection and pretreatment of high-flow pure PLA raw material in steps S1 and S2: Select stereocomposite PLA with a melt index of 150-300 g / 10 min and a molecular weight distribution index (PDI) of 1.5-2.0. The stereocomposite forms a cross-linked network during the meltblowing process, improving melt strength.

[0047] Low-temperature staged drying: Pre-crystallization at 60°C for 4 hours, followed by deep drying at 80°C for 4 hours to reduce the moisture content to ≤50ppm. This step prevents PLA hydrolysis at high temperatures, which can lead to molecular weight loss and odor.

[0048] 2. Optimization of meltblowing process parameters in step S3:

[0049] The twin-screw extruder uses a five-zone temperature control: Zone 1 is 170°C (to prevent overheating and degradation), Zone 2 is 180°C, Zone 3 is 190°C, Zone 4 is 200°C, and the die zone is 210°C. The temperature gradient design ensures uniform melt flow.

[0050] 3. Optimize the air drafting system in steps S4 and S5: the temperature difference between the hot air and the die head is less than 40°C to reduce the difference in fiber thermal history; set up a two-stage airflow system: the first stage is high-temperature air drafting to ensure fiber refinement, and the second stage is low-temperature cooling air introduced 30 mm from the spinneret to quickly solidify and shape the fiber.

[0051] 4. Multiple electret coordinated processing in step S7:

[0052] Plasma pretreatment: Argon / oxygen mixed plasma was used at a power of 1500 W to activate the fiber surface and introduce carboxyl (-COOH) and hydroxyl (-OH) polar groups.

[0053] High-voltage electrostatic electret: Under the conditions of 80kV voltage and 100mm inter-electrode distance, corona discharge is used to inject space charge.

[0054] Electron beam charge enhancement: 10kGy dose irradiation creates free radical trap sites in the PLA molecular chain, increasing the charge storage stability by more than 3 times.

[0055] 5. Humidification and conditioning process in step S8:

[0056] Ultrasonic atomization produces a 10μm water mist, which is then treated for 30 minutes at 25°C and 60% humidity. The water molecules penetrate the amorphous regions of the fibers, eliminating internal stress and making the product softer than PP meltblown fabric.

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] 1. The present invention is environmentally friendly: pure PLA raw materials do not require any additives, and the degradation rate of the product under composting conditions within 90 days is ≥95%, which is much higher than that of blended materials.

[0059] 2. The processing performance of the present invention is improved: the optimized temperature control and airflow system stabilizes the fiber diameter at 1-3μm (CV value ≤ 8%), and reduces the fiber breakage rate by 50% compared with the existing PLA melt-blown process.

[0060] 3. The invention has a breakthrough in filtration performance: the synergy of multiple electrets makes the filtration efficiency of 0.3μm particles reach 99.6%, the airflow resistance is only 70Pa, and the charge half-life is extended to 180 days.

[0061] 4. The present invention has cost advantages: eliminating the additive and premixing steps, equipment investment is reduced by 25%; the absence of banburying and solvent recovery processes reduces energy consumption by 40%. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 Schematic diagram of the process of the present invention;

[0063] Figure 2 This is a schematic diagram of the multi-electret treatment process of the present invention;

[0064] Figure 3 Schematic diagram of the preparation process of the stereocomplex of the polylactic acid resin of the present invention. DETAILED DESCRIPTION

[0065] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0066] Example 1, as Figure 1-Figure 3 As shown, a melt-blown spinning method based on pure PLA resin and multi-electret synergistic process is a production process for high-performance medical protective grade melt-blown fabrics;

[0067] S1. Using a pure polylactic acid resin (PLA) from NatureWorks with a melt index of 280 g / 10 min as raw material; the polylactic acid resin is a stereocomplex composed of left-handed polylactic acid (PLLA) and right-handed polylactic acid (PDLA) in an 80:20 ratio, and the preparation steps are as follows:

[0068] Premix drying: PLLA and PDLA were mixed in a ratio of 80:20 and vacuum dried at 80°C for 6 h;

[0069] Melt blending: Twin-screw extruder parameters: Temperature: Zone 1 175°C, Zone 2 185°C, Zone 3 195°C, Zone 4 195°C, Die 190°C; Screw speed: 250 rpm, Feed rate 5 kg / h;

[0070] Rapid cooling granulation: The melt is cooled in a water tank at 15°C and the pellet length is 2-3mm;

[0071] Annealing treatment: The particles were treated in a hot air circulation oven at 130°C for 20 min to promote the SC crystallinity to >95%.

[0072] S2. The PLA resin was dried at 65 ° C for 4 hours to a water content of 35 ppm;

[0073] S3. The dried PLA resin was added to the melt-blown equipment and melt-extruded in the temperature range of 170-220 ° C; the melt-blown equipment includes a twin-screw extruder with five temperature control zones, the extruder temperature: zone 1 175 ° C, zone 2 185 ° C, zone 3 195 ° C, zone 4 205 ° C, die head 215 ° C;

[0074] S4. The melt is extruded through a spinneret with an aperture of 0.2-0.4 mm, and the melt stream is stretched by high-speed hot air at 250°C, with a hot air pressure of 0.4 MPa and a flow rate of 2500 m / s. 3 / h;

[0075] S5. A low-temperature airflow cooling zone is set below the spinneret, with a cooling airflow temperature of 20°C and a wind speed of 12m / s;

[0076] S6. The drawn microfibers are collected on a receiving device 240 mm away from the spinneret to form a fiber web;

[0077] S7. The fiber web is subjected to multiple electret treatments, including low-temperature plasma pretreatment, high-voltage electrostatic electret treatment, and charge enhancement treatment;

[0078] S71. Low temperature plasma pretreatment: Plasma: Ar / O 2＝ 4:1, 1500W, processing 2s;

[0079] S72. High-voltage electret: Corona discharge treatment at 80 kV and 150 mm electrode distance.

[0080] S73. Charge enhancement treatment: Electron beam irradiation with an irradiation dose of 15 kGy.

[0081] S8. The fiber web after electret treatment was subjected to humidification and tempering treatment, controlling the ambient humidity to 60%, the temperature to 25°C, and the treatment time to 40 min;

[0082] S9. Rewind to obtain the finished bio-based degradable meltblown non-woven fabric.

[0083] Example 1, the performance of the prepared product is as follows:

[0084] Fiber diameter: 1.8±0.3μm

[0085] Weight: 25g / m 2

[0086] Filtration efficiency (0.3μm NaCl): 99.76%

[0087] Airflow resistance: 68Pa

[0088] Degradation rate (90 days composting): 97.2%.

[0089] Example 2 is a production process for a high-adsorptive filter material according to the present invention, which is substantially the same as Example 1, except that:

[0090] The raw material melt index is adjusted to 180g / 10min

[0091] Receiving distance increased to 280mm

[0092] The electron beam dose was increased to 25 kGy.

[0093] The performance of the finished product of Example 2 is as follows:

[0094] Fiber diameter: 4.2±0.5μm

[0095] Weight: 50g / m 2

[0096] Oil absorption rate: 18g / g

[0097] Filtration efficiency: 98.9%.

[0098] The fiber diameter of this embodiment increases the fluffiness of the finished product compared to that of embodiment 1.

[0099] The method of CN112694730A was adopted: PLA (melt index 120 g / 10 min) was added with 5% potassium sorbate, melt blended at 190°C, the die temperature was 200°C, and multiple electrets were not used. The performance comparison of the finished product is shown in the following table with those of Examples 1 and 2:

[0100]

[0101] As shown in the table above, the present invention significantly improves the filtration performance and mechanical strength of meltblown fabric while maintaining its fully biodegradable properties, without the need for any chemical modifiers, thus resolving the core flaws of the prior art. The meltblown fabric of the present invention can be widely used in the following areas: medical protection: making degradable medical masks (filter layers) and protective clothing linings; environmentally friendly filter materials: air purifier filter elements and water treatment filter materials, which can be composted after disposal; high-end sanitary materials: guide layers for baby diapers and sanitary napkins, utilizing the natural antibacterial properties of PLA; packaging adsorption materials: replacing polypropylene with oil-absorbing cotton.

[0102] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A melt-blown spinning process for biodegradable melt-blown nonwoven fabrics, characterized in that: The following steps are involved: S1 using a melt index of 150-300g / 10min pure polylactic acid resin ie PLA resin as raw material; S2. The PLA resin is dried at 60-80 ° C for 4-8 hours to a water content of ≤50ppm; S3. The dried PLA resin is added to the melt-blown equipment and melt-extruded at a temperature range of 170-220 ° C; S4. The melt is extruded through a spinneret with an aperture of 0.2-0.4 mm, and the melt stream is stretched using high-speed hot air at 230-280°C. The hot air pressure is 0.2-0.5 MPa and the flow rate is 2000-3000 m 3 / h; S5. A low-temperature airflow cooling zone is provided below the spinneret, the cooling airflow temperature is 10-25°C, and the wind speed is 5-15m / s; S6. The drawn microfibers are collected on a receiving device 150-300mm away from the spinneret to form a fiber web; S7. The fiber web is subjected to multiple electret treatments, including low-temperature plasma pretreatment, high-voltage electrostatic electret treatment, and charge enhancement treatment; S8. The electret treated fiber web is subjected to humidification and tempering treatment, and the ambient humidity is controlled at 40-70% and the temperature is 20-35 ℃; S9. Rewind to obtain the finished bio-based degradable meltblown non-woven fabric.

2. The melt-blown spinning process of a bio-based degradable melt-blown non-woven fabric according to claim 1, characterized in that: The multi-electret treatment specifically includes: S71 low-temperature plasma pretreatment: using argon / oxygen gas mixture, power 500-2000W, frequency 10-40kHz treatment conditions for 0.5-3 seconds; S72. High-voltage electret: Corona discharge treatment at 30-100 kV and an electrode distance of 50-200 mm; S73. Charge enhancement treatment: Electron beam irradiation is used with an irradiation dose of 5-30 kGy.

3. The melt-blown spinning process of a bio-based degradable melt-blown non-woven fabric according to claim 1, characterized in that: The melt-blowing equipment includes a twin-screw extruder with five temperature control zones: zone one 170-180°C, zone two 180-190°C, zone three 190-200°C, zone four 200-210°C, and die zone 210-220°C.

4. The melt-blown spinning process of a bio-based degradable melt-blown non-woven fabric according to claim 1, characterized in that: The cooling air flow is dehumidified air with a relative humidity of ≤30%. The cooling zone is 10-50 mm away from the outlet of the spinneret.

5. The melt-blown spinning process of a bio-based degradable melt-blown non-woven fabric according to claim 1, characterized in that: The receiving device is a rotary drum web forming machine with negative pressure adsorption, the negative pressure value is 500-2000 Pa, and the linear speed of the rotary drum surface is 5-30 m / min.

6. The melt-blown spinning process of a bio-based degradable melt-blown non-woven fabric according to claim 1, characterized in that: The humidification and conditioning treatment uses an ultrasonic humidification system, the water mist particle size is 5-20 μm, and the treatment time is 10-60 minutes.

7. The melt-blown spinning process of a bio-based degradable melt-blown non-woven fabric according to claim 1, characterized in that: The polylactic acid resin is a stereocomplex composed of left-handed polylactic acid PLLA and right-handed polylactic acid PDLA in a ratio of 90:10-70:

30.

8. The melt-blown spinning process of a bio-based degradable melt-blown non-woven fabric according to claim 7, characterized in that: The molecular structure design of the stereocomplex: PLLA: It is polymerized from L-lactic acid monomers to form a left-handed helical conformation; PDLA: It is formed by the polymerization of D-lactic acid monomers to form a right-handed helical conformation; After the two are melt-blended in a ratio of 90:10 to 70:30, a staggered three-dimensional network structure is formed through stereo-complex crystallization. Its crystallization temperature is 40-50°C higher than that of a single component, and the melting point is 210-230°C.

9. The melt-blown spinning process of a bio-based degradable melt-blown non-woven fabric according to claim 7, characterized in that: The preparation method of the stereocomplex: S11. Material pretreatment: PLLA and PDLA were vacuum dried at 80°C for 6 hours, with a moisture content of ≤100 ppm. The mixture is melt-blended in a twin-screw extruder according to a target ratio at a temperature of 180-200° C., a rotation speed of 200-300 rpm, and a residence time of 2-5 minutes; and 0.01-0.1 wt % of a hindered phenol antioxidant is added during the melt-blending. S12. Stereocomplex Dynamic Control: After blending, the temperature is rapidly cooled to below 100°C to inhibit homocrystallization; and annealed at 120-140°C for 10-30 minutes to promote the growth of SC crystal nuclei, with a grain size of 50-200 nm.

10. The melt-blown spinning process of a bio-based degradable melt-blown non-woven fabric according to claim 7, characterized in that: The weight average molecular weight ratio of the PLLA to the PDLA is 1:1-1:1.5, and the molecular weight distribution index is ≤1.8.

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