Degradable polylactic acid melt-blown material, preparation method thereof and melt-blown filter material

Abstract

The invention belongs to the field of non-woven fabrics, and particularly relates to a degradable polylactic acid melt-blown material, a preparation method thereof and a melt-blown filter material. The preparation method comprises the following steps: blending the poly-L-lactic acid and the small-molecular-weight poly-D-lactic acid to improve the melt index of the poly-L-lactic acid, so as to obtain a PLLA / PDLA blended material; melting and mixing the PLLA / PDLA blended material and a plasticizer at the temperature of 190-200 DEG C to obtain blended granules; and preparing the degradable polylactic acid melt-blown material from the blended granules by adopting a melt-blowing method. The degradable polylactic acid melt-blown material is a full-degradable material, has no pollution to the environment, and has better heat resistance and stability. The degradable polylactic acid melt-blown material is subjected to electrostatic electret to obtain a melt-blown filter material which can be used for a filter layer of a mask.

Description

Technical Field

[0001] The invention belongs to the field of non-woven fabrics, and in particular relates to a degradable polylactic acid melt-blown material, a preparation method thereof, and a melt-blown filter material. Background Art

[0002] Polylactic acid (PLA) is obtained by direct polycondensation of optically active lactic acid, or by first dehydration condensation of lactic acid to form cyclic lactide with corresponding optical activity, and then by ring-opening polymerization of lactide. PLA is a polylactic acid homopolymer obtained by lactic acid monomers with different optical activity, which can be divided into left-handed polylactic acid (PLLA), right-handed polylactic acid (PDLA) and racemic polylactic acid (PDLLA).

[0003] Non-woven fabrics are made of directional or random fibers and are a new generation of environmentally friendly materials. They are breathable, light, flexible, non-toxic and non-irritating. Meltblowing is a non-woven fabric processing technology that directly prepares polymers into a web. Its main working principle is to use high-speed, high-temperature airflow to gradually solidify the polymer melt into a thin stream of melt, thereby obtaining ultra-fine fibers. It has been widely used in the manufacturing process of non-woven fabrics.

[0004] At present, there are some studies on polylactic acid blended meltblown fabrics. Chinese patent CN115387023 discloses a method for preparing a TPU / PLA meltblown composite non-woven fabric, in which polylactic acid, polyurethane elastomer, compatibilizer, antioxidant, stabilizer, and plasticizer are mixed and melt-blown to obtain a TPU / PLA meltblown composite non-woven fabric, which has good hydrolysis resistance, stability, and strong mechanical properties. Chinese patent CN113403750 discloses a method for preparing a fully degradable non-woven fabric produced by a meltblown method, in which a caprolactone-lactic acid random copolymer is first prepared, and then the copolymer and polylactic acid are blended and modified and a non-woven fabric is prepared by a meltblown method. The various performance indicators of the non-woven fabric are effectively improved, and it is made of fully degradable materials and is pollution-free to the environment. In terms of improving the spinnability of polylactic acid meltblown, the existing technology mainly uses polycaprolactone, polybutylene succinate, polyhydroxybutyrate valerate and other materials to blend, but the compatibility between different materials is poor, and compatibilizers, lubricants and other ingredients need to be added, but the use of some additives will affect the degradation performance and safety performance of polylactic acid itself. Chinese patent CN115323614A discloses a method for preparing a tough and fully degradable polylactic acid meltblown cloth, which includes two-component polylactic acid with different melt indexes and an electret masterbatch prepared in a corresponding proportion. The present invention adopts the self-toughening principle, does not require granulation, and has a simple and easy-to-operate preparation process. It can be applied to large-scale production and the materials used are all degradable materials. The biodegradability rate of the prepared polylactic acid meltblown cloth can be close to 100%. The polylactic acid self-toughening meltblown non-woven fabric has poor heat resistance and is easily hydrolyzed, resulting in reduced filtration efficiency during transportation and storage of the non-woven fabric. Therefore, while improving the processing performance of polyemulsion meltblown, it is also necessary to improve its stability to ensure the filtration performance of the melt-blown nonwoven fabric. Summary of the invention

[0005] In view of the shortcomings and deficiencies of the above-mentioned prior art, the present invention provides a degradable polylactic acid meltblown material and a preparation method thereof and a meltblown filter material. The preparation method can solve the meltblowing molding problem of polylactic acid material, and the obtained meltblown material has better heat resistance and stability.

[0006] To achieve the above object, the present invention is implemented through the following technical solutions:

[0007] The first aspect of the present invention provides a method for preparing a degradable polylactic acid melt-blown material, the preparation method comprising the following steps:

[0008] S1. Blending L-polylactic acid with low molecular weight D-polylactic acid to obtain a PLLA / PDLA blend;

[0009] S2. melt-mixing the PLLA / PDLA blend and the plasticizer at 190°C-200°C to obtain a blended pellet;

[0010] S3. The blended pellets are prepared by melt-blowing method to obtain the degradable polylactic acid melt-blown material.

[0011] As a preferred embodiment of the method for preparing the degradable polylactic acid meltblown material of the present invention, in step S1, the L-polylactic acid and the low molecular weight D-polylactic acid are dried to a water content of ≤100 ppm before use.

[0012] As a preferred embodiment of the method for preparing the degradable polylactic acid melt-blown material of the present invention, the weight average molecular weight of the low molecular weight dextrorotatory polylactic acid is 20,000-50,000.

[0013] As a preferred embodiment of the method for preparing the degradable polylactic acid melt-blown material of the present invention, the weight average molecular weight of the L-polylactic acid is 80,000-120,000.

[0014] As a preferred embodiment of the method for preparing the degradable polylactic acid melt-blown material of the present invention, the content of low molecular weight dextrorotatory polylactic acid in the PLLA / PDLA blend is 0.1-5wt%.

[0015] As a preferred embodiment of the method for preparing the degradable polylactic acid melt-blown material of the present invention, the plasticizer is polyethylene glycol.

[0016] As a preferred embodiment of the method for preparing the degradable polylactic acid melt-blown material of the present invention, the plasticizer is polyethylene glycol with a weight average molecular weight of 10,000 to 30,000.

[0017] As a preferred embodiment of the method for preparing the degradable polylactic acid melt-blown material of the present invention, the mass ratio of the plasticizer to the PLLA / PDLA blend is (5-10):100.

[0018] As a preferred embodiment of the method for preparing the degradable polylactic acid melt-blown material of the present invention, step S3 is specifically: adding the blended pellets into a twin-screw extruder, extruding, melting and plasticizing, and then ejecting them from the die spinneret holes of the spinneret assembly at 190-200°C, and stretching them by a hot air flow of 210-230°C and cooling them by cold air on both sides of the die to form ultrafine fibers, which are condensed onto a roller under the action of the air flow to form a degradable polylactic acid melt-blown material.

[0019] As a preferred embodiment of the method for preparing the degradable polylactic acid meltblown material of the present invention, in step S3, the receiving distance of the roller is 20 cm.

[0020] As a preferred embodiment of the method for preparing the degradable polylactic acid meltblown material of the present invention, the average fineness of the ultrafine fibers is 0.8-1.5 μm.

[0021] The second aspect of the present invention also provides a degradable polylactic acid melt-blown material prepared by the above-mentioned method for preparing the degradable polylactic acid melt-blown material.

[0022] The third aspect of the present invention further provides a melt-blown filter material, which is obtained by subjecting the above-mentioned degradable polylactic acid melt-blown material to an electrostatic electret treatment.

[0023] The degradable polylactic acid melt-blown material and the preparation method thereof according to the embodiments of the present invention have at least one of the following advantages:

[0024] (1) The PLLA / PDLA blend obtained by blending high molecular weight PLLA and low molecular weight PDLA in the present invention has a higher melt index, thereby enabling its melt-blown spinning process, solving the melt-blown molding problem of conventional polylactic acid materials.

[0025] (2) The PLLA / PDLA blend obtained by blending high molecular weight PLLA and low molecular weight PDLA in the present invention not only has a higher melt index, but is also easier to draw and thin during the spinning process, thereby making it easier for PLLA and PDLA to form a stereocomposite structure, further improving the heat resistance and stability of the obtained non-woven fabric.

[0026] (3) The raw materials used in the preparation method provided by the present invention are all fully degradable raw materials, and the preparation process is simple and easy to operate.

[0027] (4) The 0.5 μm particle filtration efficiency of the degradable polylactic acid melt-blown material of the present invention is 95-99.9%, the breaking strength is 6-20 N / 50 mm, the breaking elongation is 60-100%, and the degradation period in sludge is 80-120 days. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present invention are described clearly and completely below. 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 creative work are within the scope of protection of the present invention.

[0029] Example 1

[0030] (1) Weigh 0.01 kg of PDLA with a molecular weight of 20,000 and 9.99 kg of PLLA with a molecular weight of 80,000, dry them in an oven at 90°C, and blend them using a high-speed mixer.

[0031] (2) The blend obtained in step (1) and 0.5 kg of a PEG plasticizer having a weight average molecular weight of 10,000 are added to a twin-screw extruder, and melt-extruded and granulated at 190° C. to obtain blended granules.

[0032] (3) The blended pellets obtained in step (2) are extruded and melted in a twin-screw extruder, and ejected from the die spinneret hole of the spinneret assembly at 190°C, and are stretched by a hot air flow at 210°C and cooled by cold air on both sides of the die to form ultrafine fibers, which are condensed on a roller under the action of the air flow to form a non-woven fabric and subjected to an electrostatic electret treatment. The obtained fully degradable polylactic acid melt-blown non-woven fabric has a thickness of 0.1 mm, an average fiber fineness of 1.5 μm, a breaking strength of 6 N / 50 mm, an elongation at break of 100%, a 0.5 μm particle filtration efficiency of 95%, a 0.5 μm particle filtration efficiency of 92% after storage for 6 months, and a degradation period in sludge of 94 days.

[0033] Example 2

[0034] (1) Weigh 0.05 kg of PDLA with a molecular weight of 30,000 and 9.95 kg of PLLA with a molecular weight of 100,000, dry them in an oven at 90° C., and blend them using a high-speed mixer.

[0035] (2) The blend obtained in step (1) and 0.7 kg of a PEG plasticizer having a weight average molecular weight of 10,000 are added to a twin-screw extruder, and melt-extruded and granulated at 190° C. to obtain blended granules.

[0036] (3) The blended pellets obtained in step (2) are extruded and melted in a twin-screw extruder, and ejected from the die spinneret hole of the spinneret assembly at 190°C, and are stretched by a hot air flow at 210°C and cooled by cold air on both sides of the die to form ultrafine fibers, which are condensed on a roller under the action of the air flow to form a non-woven fabric and subjected to an electrostatic electret treatment. The obtained fully degradable polylactic acid melt-blown non-woven fabric has a thickness of 0.23 mm, an average fiber fineness of 1.3 μm, a breaking strength of 16.35 N / 50 mm, an elongation at break of 89.12%, a 0.5 μm particle filtration efficiency of 98.3%, a 0.5 μm particle filtration efficiency of 95.1% after storage for 6 months, and a degradation period of 102 days in sludge.

[0037] Example 3

[0038] (1) Weigh 0.1 kg of PDLA with a molecular weight of 40,000 and 9.9 kg of PLLA with a molecular weight of 10, dry them in an oven at 90° C., and blend them using a high-speed mixer.

[0039] (2) The blend obtained in step (1) and 0.8 kg of a PEG plasticizer having a weight average molecular weight of 20,000 are added to a twin-screw extruder, and melt-extruded and granulated at 195° C. to obtain blended granules.

[0040] (3) The blended pellets obtained in step (2) are extruded and melted in a twin-screw extruder, and ejected from the die spinneret hole of the spinneret assembly at 195°C, and are stretched by a hot air flow at 220°C and cooled by cold air on both sides of the die to form ultrafine fibers, which are condensed on a roller under the action of the air flow to form a non-woven fabric and subjected to an electrostatic electret treatment. The obtained fully degradable polylactic acid melt-blown non-woven fabric has a thickness of 0.25 mm, an average fiber fineness of 1.1 μm, a breaking strength of 18.54 N / 50 mm, an elongation at break of 85.88%, a 0.5 μm particle filtration efficiency of 99.1%, a 0.5 μm particle filtration efficiency of 95.9% after storage for 6 months, and a degradation period of 80 days in sludge.

[0041] Example 4

[0042] (1) Weigh 0.3 kg of PDLA with a molecular weight of 50,000 and 9.7 kg of PLLA with a molecular weight of 120,000, dry them in an oven at 90° C., and blend them using a high-speed mixer.

[0043] (2) The blend obtained in step (1) and 0.9 kg of a PEG plasticizer having a weight average molecular weight of 30,000 are added to a twin-screw extruder, and melt-extruded and granulated at 200° C. to obtain blended granules.

[0044] (3) The blended pellets obtained in step (2) are extruded and melted in a twin-screw extruder, and ejected from the die spinneret hole of the spinneret assembly at 200°C, and are stretched by a hot air flow at 230°C and cooled by cold air on both sides of the die to form ultrafine fibers, which are condensed on a roller under the action of the air flow to form a non-woven fabric and subjected to an electrostatic electret treatment. The obtained fully degradable polylactic acid melt-blown non-woven fabric has a thickness of 0.5 mm, an average fiber fineness of 1 μm, a breaking strength of 20 N / 50 mm, an elongation at break of 60%, a 0.5 μm particle filtration efficiency of 99.3%, a 0.5 μm particle filtration efficiency of 96.4% after storage for 6 months, and a degradation period of 120 days in sludge.

[0045] Example 5

[0046] (1) Weigh 0.5 kg of PDLA with a molecular weight of 50,000 and 9.5 kg of PLLA with a molecular weight of 120,000, dry them in an oven at 90°C, and blend them using a high-speed mixer.

[0047] (2) The blend obtained in step (1) and 1 kg of PEG plasticizer with a weight average molecular weight of 30,000 are added to a twin-screw extruder, and melt-extruded and granulated at 200° C. to obtain blended granules.

[0048] (3) The blended pellets obtained in step (2) are extruded and melted in a twin-screw extruder, and ejected from the die spinneret hole of the spinneret assembly at 200°C, and are stretched by a hot air flow at 230°C and cooled by cold air on both sides of the die to form ultrafine fibers, which are condensed on a roller under the action of the air flow to form a non-woven fabric and subjected to an electrostatic electret treatment. The obtained fully degradable polylactic acid melt-blown non-woven fabric has a thickness of 0.36 mm, an average fiber fineness of 0.8 μm, a breaking strength of 19.7 N / 50 mm, an elongation at break of 80.24%, a 0.5 μm particle filtration efficiency of 99.9%, a 0.5 μm particle filtration efficiency of 97% after storage for 6 months, and a degradation period of 115 days in sludge.

[0049] Comparative Example 1

[0050] (1) Weigh 2 kg of PDLA with a molecular weight of 80,000 and 8 kg of PLLA with a molecular weight of 80,000, dry them in an oven at 90° C., and blend them using a high-speed mixer.

[0051] (2) The blend obtained in step (1) and 0.8 kg of a PEG plasticizer having a weight average molecular weight of 20,000 are added to a twin-screw extruder, and melt-extruded and granulated at 195° C. to obtain blended granules.

[0052] (3) The blended pellets obtained in step (2) are extruded and melted in a twin-screw extruder, and ejected from the die spinneret hole of the spinneret assembly at 200°C, and are stretched by a hot air flow at 210°C and cooled by cold air on both sides of the die to form fibers, and the ultrafine fibers are condensed on a roller under the action of the air flow to form a non-woven fabric, which is then electrostatically charged. The obtained fully degradable polylactic acid melt-blown non-woven fabric has a thickness of 0.25 mm, an average fiber fineness of 8.6 μm, a breaking strength of 5.88 N / 50 mm, an elongation at break of 57.49%, a 0.5 μm particle filtration efficiency of 40%, a 0.5 μm particle filtration efficiency of 37% after storage for 6 months, and a degradation period of 105 days in sludge.

[0053] Comparative Example 2

[0054] Weigh 10 kg of PLLA with a molecular weight of 100,000 and dry it in an oven at 90°C. Add the PLLA particles into a twin-screw extruder for extrusion melting. Pure PLLA cannot be made into non-woven fabrics by melt-blowing.

[0055] Comparative Example 3

[0056] 10kg of PLLA with a molecular weight of 100,000 was weighed and dried in an oven at 90°C. PLLA particles and 0.8kg of PEG with a weight average molecular weight of 20,000 were added to a twin-screw extruder for melt blending to obtain a blended pellet. The blended pellet was then added to a twin-screw extruder for extrusion, melt plasticization, and ejected from the die spinneret hole of the spinneret assembly at 200°C. After being drawn by a hot air flow at 230°C and cooled by cold air on both sides of the die, ultrafine fibers were formed. The ultrafine fibers condensed on the roller under the action of the air flow to form a non-woven fabric and subjected to electrostatic electret treatment. The thickness of the obtained fully degradable polylactic acid melt-blown non-woven fabric was 0.3mm, the average fiber fineness was 1.2μm, the breaking strength was 16.7N / 50mm, the breaking elongation was 59%, and the degradation period in sludge was 92 days. The filtration efficiency of 0.5μm particles was 96.5%, but the filtration efficiency of 0.5μm particles was 43% after storage for 6 months.

[0057] Although some embodiments of the present general inventive concept have been shown and described, it will be appreciated by those skilled in the art that changes may be made to these embodiments without departing from the principles and spirit of the present general inventive concept, the scope of which is defined in the claims and their equivalents.

Claims

1. A method for preparing a degradable polylactic acid melt-blown material, characterized in that: The preparation method comprises the following steps: S1. Blending L-polylactic acid with low molecular weight D-polylactic acid to obtain a PLLA / PDLA blend; S2. melt-mixing the PLLA / PDLA blend and the plasticizer at 190°C-200°C to obtain a blended pellet; S3. The blended pellets are prepared by melt-blowing method to obtain the degradable polylactic acid melt-blown material.

2. The preparation method according to claim 1, characterized in that: The weight average molecular weight of low molecular weight dextrorotatory polylactic acid is 20,000-50,000.

3. The preparation method according to claim 2, characterized in that: The weight average molecular weight of the L-polylactic acid is 80,000-120,000.

4. The preparation method according to claim 3, characterized in that: In the PLLA / PDLA blend, the content of low molecular weight dextrorotatory polylactic acid is 0.1-5wt%.

5. The preparation method according to claim 1, characterized in that: The plasticizer is polyethylene glycol.

6. The preparation method according to claim 5, characterized in that: The mass ratio of the plasticizer to the PLLA / PDLA blend is (5-10):

100.

7. The preparation method according to claim 1, characterized in that: Step S3 is specifically as follows: adding the blended pellets into a twin-screw extruder, extruding, melting and plasticizing, and then ejecting them from the die spinneret holes of the spinneret assembly at 190-200°C, and stretching them by a hot air flow at 210-230°C and cooling them by cold air on both sides of the die to form ultrafine fibers, which are condensed onto a roller under the action of the air flow to form a degradable polylactic acid meltblown material.

8. The preparation method according to claim 7, characterized in that: The average fineness of the ultrafine fibers is 0.8-1.5 μm.

9. The degradable polylactic acid melt-blown material prepared by the preparation method according to any one of claims 1 to 8.

10. A melt-blown filter material, characterized in that: The melt-blown filter material is obtained by subjecting the degradable polylactic acid melt-blown material according to claim 9 to an electrostatic electret treatment.