A PLA melt-blown filter material with low water absorption and preparation method thereof

Abstract

The present invention relates to a PLA melt-blown filter material with low water absorption and a preparation method thereof, comprising the following components by weight: 100 parts of PLA resin, 15-30 parts of a bio-based polycarbonate toughening agent, 4-10 parts of a compatibilizer, 2-5 parts of a nucleating agent, and 0.5-3 parts of an antibacterial agent. The invention also discloses a preparation method for the PLA melt-blown filter material. The raw materials of the invention are widely available, inexpensive, and environmentally friendly. The material has excellent biodegradability and mechanical properties, and also has good flexibility, thermal stability, low water absorption, antibacterial properties, and electret properties. The preparation method uses simple equipment, a simple process, low energy consumption, and is suitable for industrial production and application.

Description

Technical Field

[0001] The present invention relates to the field of melt-blown filter materials, in particular to a melt-blown filter material of PLA with low water absorption and a preparation method thereof. Background Art

[0002] Most masks are made of polymer materials, which can take hundreds of years to fully degrade, potentially spreading viruses. Conventional landfill, incineration, or disposal can pollute soil, air, and water, severely damaging the ecological environment. However, centralized recycling and disinfection are difficult to implement, making the recycling and reuse of discarded masks challenging. Therefore, using biodegradable materials to make masks can effectively alleviate the pressure on the ecological environment caused by discarded masks.

[0003] Polylactic acid (PLA), also known as polylactide, is an aliphatic thermoplastic polyester and one of the earliest commercially developed bio-based, biodegradable, and biocompatible polymers. PLA can be prepared through direct polycondensation of lactic acid monomers or ring-opening polymerization of cyclic lactide dimers. However, PLA also suffers from shortcomings such as low melt strength, slow crystallization rate, low operating temperature, and heat distortion temperature (HDT), which hinder its application. Furthermore, PLA is brittle, with a low elongation at break and a glass transition temperature (Tg) of only 55-60°C. Combined with PLA's high water absorption, these shortcomings significantly limit its use in face mask materials.

[0004] However, in the existing technologies for modifying polylactic acid to improve its shortcomings, the added substances are not completely compatible with polylactic acid (the blend has only one glass transition temperature Tg), the toughening modification effect is not ideal, and the blend still contains a large amount of non-degradable organic components, which cannot achieve the ideal degree of biodegradation. Summary of the Invention

[0005] In view of the existing deficiencies, the present invention provides a PLA melt-blown filter material with low water absorption and a preparation method thereof.

[0006] The technical solution adopted by the present invention to solve the technical problem is: a PLA melt-blown filter material with low water absorption, comprising the following components by mass: 100 parts of PLA resin, 15-30 parts of a bio-based polycarbonate toughening agent with a number average molecular weight (Mn) of 15,000 to 35,000 g / mol, 4-10 parts of a compatibilizer, 2-5 parts of a nucleating agent, and 0.5-3 parts of an antibacterial agent; wherein the PLA resin comprises 50-65 parts of a left-handed PLA resin with a number average molecular weight (Mn) of 45,000 to 120,000 g / mol and 35-50 parts of a number average molecular weight (Mn) of a bio-based polycarbonate toughening agent. n) is a dextrorotatory PLA resin of 10,000 to 80,000 g / mol; the compatibilizer is a binary copolymer of lactide and trimethylene carbonate with a number average molecular weight (Mn) of 25,000 to 34,000 g / mol; the nucleating agent is a degradable polyethylene glycol-modified hyperbranched polyether ester with a number average molecular weight (Mn) of 7,500 to 24,000 g / mol; the antibacterial agent is titanium dioxide-modified hydroxyapatite with an average particle size of 100 nm to 200 nm; the bio-based polycarbonate toughening agent is a bio-based isosorbide-type polycarbonate toughening agent having the following structural formula: Wherein R is any one of dimethyl carbonate, diethyl carbonate, isomannide, n-butylene glycol, n-hexylene glycol, n-octanediol, n-decanediol, and tartaric acid derivatives, and m and n are the numbers of each monomer polymerized.

[0007] Preferably, the mass ratio of lactide to trimethylene carbonate is 20:80 to 70:30.

[0008] A method for preparing a PLA melt-blown filter material with low water absorption, using the components described in any of the above filter materials, and the steps are as follows:

[0009] S1, drying and pre-treating the bio-based polycarbonate toughening agent as raw material A;

[0010] S2, drying and pre-treating the PLA resin and the compatibilizer respectively;

[0011] S3, mixing the dried pretreated PLA resin, the compatibilizer, the nucleating agent, and the antibacterial agent to form raw material B;

[0012] S4, mixing raw material A and raw material B to prepare modified PLA resin;

[0013] S5, melt-blowing the modified PLA resin to prepare a PLA melt-blown filter material.

[0014] Preferably, the method further includes step S6 of subjecting the prepared PLA melt-blown filter material to an electret treatment.

[0015] The present invention has the following beneficial effects: it uses a polymer nucleating agent to form a stereocrystalline blend of PLA resin, significantly improving heat resistance. The bio-based polycarbonate, used as a toughening agent and combined with a compatibilizer, significantly improves blending processing toughness and further enhances heat resistance. Furthermore, the antimicrobial agent not only exhibits good antimicrobial properties but also exhibits excellent biocompatibility and biodegradability. The method for preparing low-water-absorption PLA melt-blown filter material features inexpensive equipment, a simple process, and low energy consumption, making it easy to industrialize. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a scanning electron microscope image of the fiber of the filter material according to an embodiment of the present invention; DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present application are clearly and completely described below. Obviously, the embodiments described are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. The experimental methods used in the following examples are all conventional methods unless otherwise specified; the materials, reagents, etc. used, unless otherwise specified, can be obtained from commercial channels.

[0018] In order to better understand the technical content of the present invention, the following specific examples are provided to further illustrate the present invention. It should be noted that in the embodiments of the present invention, the performance characterization method used in the present invention is as follows:

[0019] Performance characterization of low water absorption PLA melt-blown filter material:

[0020] (1) Breaking strength and elongation at break

[0021] Using an electronic textile strength tester (HD026N, Nantong Hongda Experimental Instrument Co., Ltd.), in accordance with GB / T 24218.3-2010 (Textiles—Nonwoven Fabrics—Test Methods—Part 3: Determination of Breaking Strength and Elongation at Break (Strip Method)), low-water-absorption PLA meltblown filter material samples were subjected to longitudinal and transverse tensile testing. The clamping distance was 10 cm and the tensile speed was 100 mm / min. Five longitudinal and transverse tensile tests were performed on each sample, and the average value was calculated.

[0022] (2) Determination of fiber morphology and structure

[0023] The surface and cross-sectional morphologies of the PLA melt-blown filter material with low water absorption were observed using an electron microscope (Phenom Particle X, Thermo Fisher Scientific).

[0024] (3) Heat deformation temperature (HDT)

[0025] The heat deflection temperature of the specimens was measured using a heat deflection temperature tester according to ASTM D648-2018 Standard Test Method for Deflection Temperature of Plastics Under Flexural Load in the Edgewise Position. The specimen thickness was 3.2 mm and the load was 1.8 MPa.

[0026] (4) Filtration efficiency and airflow resistance

[0027] The test was conducted in accordance with the standards in Section 5.4 of GB 19083-2010 Technical Requirements for Medical Protective Masks, using 0.075±0.02μm NaCl particles, a gas flow rate of 85L / min, and a test environment with a temperature and humidity of approximately 23°C and 30%, respectively.

[0028] (5) Breathability

[0029] Refer to GB / T5453-1997 "Test for Air Permeability of Textile Fabrics" to test the air permeability, and select 100Pa as the pressure difference.

[0030] (6) Water contact angle

[0031] Contact angles were measured using a contact angle meter equipped with a goniometer and a constant temperature device. Low-water-absorption PLA resin was repeatedly heat-pressed at 200°C into a flat film 20 ± 3 μm thick. A 5 μl droplet of distilled water was dispensed from a microsyringe with a 0.1 μl accuracy and dropped onto the film surface. The droplet profile was observed under a microscope at 10x magnification. Contact angles were measured at five locations on each sample surface, and the average was calculated.

[0032] (7) Water absorption

[0033] Weigh a certain mass W1 (approximately 2.0 g) of vacuum-dried polymer membrane to a constant weight and place it in a cell culture dish. Add PBS (phosphate buffer solution) at pH 7.4 and soak at (37.0 ± 0.5)°C for 24 hours. Use filter paper to absorb the water on the membrane surface, weigh W1, and then vacuum-dry to a constant weight. Weigh W2. For W2, the water absorption rate Ra = (W2 - W1) / W1 × 100%. Repeat the test three times and take the average value.

[0034] (8) Relative biodegradation rate (90 days) and half-life

[0035] The 90-day relative biodegradation rate and half-life (relative biodegradation rate 50%) test was performed with reference to ASTM D5511-2018 Standard Test Method for Determining Anaerobic Biodegradation of Plastic Materials Under High-Solids Anaerobic-Digestion Conditions, and microcrystalline cellulose was used as the positive control.

[0036] Unless otherwise specified, the "parts" in the present invention refer to "parts by mass"

[0037] In the present invention, a PLA melt-blown filter material with low water absorption rate comprises the following components in parts by mass: 100 parts of PLA resin, 15-30 parts of bio-based polycarbonate toughening agent, 4-10 parts of compatibilizer, 2-5 parts of nucleating agent, and 0.5-3 parts of antibacterial agent. For example, 100 parts of PLA resin, 20-25 parts of bio-based polycarbonate toughening agent, 6-8 parts of compatibilizer, 3-4 parts of nucleating agent, and 1-2 parts of antibacterial agent are selected, and preferably the PLA resin is a mixture of 50-65 parts of left-handed PLA resin and 35-50 parts of right-handed PLA resin. In actual production, In the production process, 55-60 parts of left-handed PLA resin (PLLA) and 40-45 parts of right-handed PLA resin (PDLA) are selected, the number average molecular weight (Mn) of the left-handed PLA resin is 45,000-120,000 g / mol, and the number average molecular weight (Mn) of the right-handed PLA resin is 10,000-80,000 g / mol, or the number average molecular weight (Mn) of the left-handed PLA resin is 79,000-92,000 g / mol, and the number average molecular weight (Mn) of the right-handed PLA resin is 40,000-54,000 g / mol.

[0038] Bio-based polycarbonate toughening agent is a bio-based isosorbide-type polycarbonate toughening agent with the following structural formula: Wherein R is an aliphatic monomer, such as R is any one of dimethyl carbonate, diethyl carbonate, isomannide, n-butanediol, n-hexanediol, n-octanediol, n-decanediol, and tartaric acid derivatives, m and n are the number of polymerizations of each monomer, preferably R is dimethyl carbonate or hexanediol, and the number average molecular weight (Mn) of the bio-based polycarbonate is 15,000 to 35,000 g / mol or 19,000 to 30,000 g / mol.

[0039] The compatibilizer is a binary copolymer of lactide and trimethylene carbonate, and their mass ratio is 20:80 to 70:30. Lactide uses D-lactide or L-lactide. For example, the mass ratio of lactide to trimethylene carbonate (TMC) is 20:80 to 60:40, and the number average molecular weight (Mn) of the compatibilizer is 25,000 to 34,000 g / mol, or the mass ratio of lactide to trimethylene carbonate (TMC) is 40:60 to 50:50, and the number average molecular weight (Mn) of the compatibilizer is 29,000 to 32,000 g / mol.

[0040] The nucleating agent is a degradable polyethylene glycol-modified hyperbranched polyether ester, and the number average molecular weight (Mn) of the nucleating agent is 7500-24000 g / mol or 14000-17000 g / mol.

[0041] The antibacterial agent is titanium dioxide modified hydroxyapatite, which is titanium dioxide modified hydroxyapatite with low water absorption rate, and has an average particle size of 100nm to 200nm. In practice, the average particle size is selected to be 25 to 45nm or 30 to 40nm.

[0042] The relative biodegradability of this filter material is ≥95%, far exceeding that of commercially available biodegradable products and exceeding the biodegradability requirements of GB / T 38082-2019 Biodegradable Plastic Shopping Bags. With the exception of the antimicrobial agent, which is an inorganic substance (but at a low concentration), all other ingredients, such as PLA resin, toughening agent, compatibilizer, and nucleating agent, are bio-based raw materials and are all fully biodegradable. By combining high-molecular-weight left-handed PLA resin (PLLA) and low-molecular-weight right-handed PLA resin (PDLA), and with the presence of a polymer nucleating agent, a degradable hyperbranched polyether ester (PEG), stereocrystalline blends are easily induced to form. This significantly increases the melting point and heat distortion temperature of the blend. This is because the molecular chains of the different enantiomers of PLLA and PDLA are arranged in a coordinated, alternating pattern, resulting in the formation of only high-melting-point sc crystals during the heating and melt crystallization process, significantly improving heat resistance.

[0043] Bio-based polycarbonate is used as a toughening agent in combination with a copolymer compatibilizer to significantly improve the toughness of the blending process and further enhance heat resistance. Biodegradable bio-based isosorbide-based polycarbonate is used as a toughening agent. It is an aliphatic polycarbonate with a wide range of raw material sources and is environmentally friendly, non-toxic and harmless. It improves compatibility with PLA resin and significantly reduces the water absorption rate of PLA materials. It also has excellent wear resistance and durability, not only reducing a large amount of carbon footprint and fossil energy consumption, but also being biodegradable and causing no environmental pollution. The lactide unit is the same as the main chain unit of PLA resin, while trimethylene carbonate (TMC) is compatible with the R unit of the toughening agent. This solves the problem that traditional polycarbonate and PLA resin directly blended together have poor interfacial compatibility and phase separation. In addition, PC has a high melt viscosity and high processing temperature, which increases the processing difference with PLA. While increasing the melt viscosity of PLA resin, its melt index is reduced, solving the problem that PLA / PC composites cannot be used in meltblown materials.

[0044] The use of degradable polyethylene glycol-modified hyperbranched polyether ester as a nucleating agent makes the crystals obtained from the blend larger and the lattice more complete. On the one hand, it has excellent biodegradability and can induce PLLA and PDLA blends to form stereostructures with high crystallization temperatures. On the other hand, due to the special structure of the hyperbranched resin, it can penetrate into the molecular chains of the blend and slip, dispersing evenly, significantly reducing the forces between the molecular chains, driving the rapid movement of the molecular chains, reducing the processing temperature and system viscosity, and improving the melt index and lubrication properties.

[0045] On this basis, titanium dioxide-coated nano-hydroxyapatite is used as an antibacterial agent. Nano-hydroxyapatite has excellent biocompatibility and bioactivity, a large specific surface area, and a good reinforcing effect on the blend. It not only has good antibacterial properties, but also has good biocompatibility and biodegradability. The surface-coated nano-titanium dioxide has electret properties. After electret polarization treatment, the polarized charge can be stably stored in the core-shell structure formed by the internal hydroxyapatite and the external titanium dioxide. Under the action of ultraviolet light, it has excellent antibacterial properties, and the filtration efficiency and antibacterial properties are further improved. The hydroxyapatite inside the titanium dioxide can form a composite nano-spherical structure with the titanium dioxide on the surface. As an electret material, it can store polarized charges stably for a long time, which is particularly suitable for application in air filtration / antibacterial materials, and is particularly suitable for application in the meltblown layer of masks.

[0046] A method for preparing a PLA melt-blown filter material with low water absorption, using the components described in any of the above filter materials, and the steps are as follows:

[0047] S1, drying and pre-treating the bio-based polycarbonate toughening agent as raw material A, that is, drying the bio-based polycarbonate toughening agent in a forced air oven at a temperature of 80-110° C. for 4-8 hours;

[0048] Example 1: 15 parts of a bio-based polycarbonate toughening agent, a copolymer of isosorbide and dimethyl carbonate, Mn = 15000 g / mol, prepared according to Table 2-2 of Li Qian's doctoral dissertation "Synthesis and Modification of Isosorbide-Based Polycarbonate" at the University of Science and Technology of China, with a treatment temperature of 80°C and drying for 8 hours;

[0049] Example 2: 30 parts of bio-based polycarbonate, a copolymer of isosorbide and butanediol, Mn = 35000 g / mol, treated at 110°C and dried for 4 hours;

[0050] Example 3: 20 parts of bio-based polycarbonate, a copolymer of isosorbide and 1,4-cyclohexanedimethanol, Mn = 19000 g / mol, treated at 100°C and dried for 5 hours;

[0051] Example 4: 25 parts of bio-based polycarbonate, a copolymer of isosorbide and hexanediol, Mn = 30000 g / mol, treatment temperature is 90 ° C, and drying is 6h;

[0052] S2, pre-treating the PLA resin and the compatibilizer by drying, respectively: pre-treating the PLA resin by drying in a blast oven at a temperature of 80-100° C. for 6-12 hours; pre-treating the compatibilizer by drying in a blast oven at a temperature of 80-100° C. for 4-8 hours;

[0053] Example 1: PLA resin was selected as a mixture of 50 parts of left-handed PLA resin (PLLA) and 50 parts of right-handed PLA resin (PDLA). The left-handed PLA resin was homemade, with reference to Section 3.3.3 of the master's thesis "Synthesis of Poly L-lactic Acid (PLLA) for Biomedical Materials" by Wang Zhenping of Central South University. The initiator dosage was 0.06%, the polymerization temperature was 180°C, the polymerization time was 48h, and Mn=45000g / mol. The right-handed PLA resin was homemade, with reference to Section 3.2 of the master's thesis "Study on the Structure and Properties of Polylactic Acid Blends" by Yang Shunyi of Beijing University of Chemical Technology. .1 part, Mn = 10000 g / mol; treatment temperature is 80 ° C, drying for 6 hours; 4 parts of a compatibilizer, which is a binary copolymer of L-lactide and trimethylene carbonate (TMC), the mass ratio of lactide to trimethylene carbonate (TMC) is 20:80, and the number average molecular weight (Mn) of the compatibilizer is 29000 g / mol. The preparation method is based on sample 2# in Section 2.2.5 of Xiao Kai's master's thesis "Synthesis and Characterization of Trimethylene Carbonate-Lactide Copolymer and Study on Its Drug Controlled Release System" at Peking Union Medical College, treatment temperature is 80 ° C, and drying is 8 hours;

[0054] Example 2: PLA resin is 65 parts of left-handed PLA resin (PLLA) and 35 parts of right-handed PLA resin, wherein the left-handed PLA resin is homemade as in Example 1, and the right-handed PLA resin is from Purapol of the Netherlands, D99max, Mn=80000 g / mol, the treatment temperature is 100 ° C, and it is dried for 6 hours; 10 parts of a compatibilizer, which is a binary copolymer of D-lactide and trimethylene carbonate (TMC), with a mass ratio of 50:50, and the number average molecular weight (Mn) of the compatibilizer is 34000 g / mol. The preparation method is according to sample 3# in section 2.2.5 of Xiao Kai's master's thesis "Synthesis and Characterization of Trimethylene Carbonate-Lactide Copolymer and Research on Its Drug Controlled Release System" of Peking Union Medical College, the treatment temperature is 100 ° C, and it is dried for 4 hours;

[0055] Example 3: PLA resin is a mixture of 55 parts of left-handed PLA resin (PLLA) and 45 parts of right-handed PLA resin (PDLA), left-handed PLA resin, Natureworks, USA, 4032D, Mn = 92000 g / mol, right-handed PLA resin, Purapol, Netherlands, D0710, Mn = 40000 g / mol, treatment temperature, 85 ° C, drying for 10 hours; 6 parts of compatibilizer, a binary copolymer of L-lactide and trimethylene carbonate (TMC), a mass ratio of 70:30, a number average molecular weight (Mn) of 25000 / mol, and the preparation method is according to sample 4# in section 2.2.5 of Xiao Kai's master's thesis "Synthesis and Characterization of Trimethylene Carbonate-Lactide Copolymer and Study on Its Drug Controlled Release System" of Peking Union Medical College, treatment temperature 85 ° C, and drying for 6 hours;

[0056] Example 4: PLA resin is 60 parts of left-handed PLA resin (PLLA) and 40 parts of right-handed PLA resin (PDLA), left-handed PLA resin, Purapol Company of the Netherlands, L100LXS, Mn = 79000 g / mol, right-handed PLA resin, Shanghai Academy of Sciences Biomaterials Company, PDLA, Mn = 54000 g / mol, treatment temperature, 90 ° C, drying 9h; 8 parts of compatibilizer, a binary copolymer of D-lactide and trimethylene carbonate (TMC), mass ratio of 60:40, number average molecular weight (Mn) of 32000 g / mol; preparation method refers to sample 4# in section 2.2.5 of Xiao Kai's master's thesis "Synthesis, Characterization and Drug Controlled Release System of Trimethylene Carbonate-Lactide Copolymer" of Peking Union Medical College, treatment temperature 90 ° C, drying 5h;

[0057] S3, mixing the dried pretreated PLA resin, the compatibilizer, the nucleating agent, and the antimicrobial agent to form raw material B. The nucleating agent and the antimicrobial agent are stored at room temperature. They are weighed according to their mass fractions and added to a high-speed mixer in sequence. The mixture is stirred at room temperature at high speed for 10 minutes and then removed to form raw material B.

[0058] Example 1: 2 parts of nucleating agent and 0.5 parts of antibacterial agent, the nucleating agent is a degradable polyethylene glycol modified hyperbranched polyether ester, homemade, Mn = 7500g / mol, prepared according to Example 1 in CN 101235134 "Degradable polyethylene glycol modified hyperbranched polyether ester and its preparation method"; the antibacterial agent is low water absorption titanium dioxide modified hydroxyapatite, with an average particle size of 25nm, prepared according to the paper "The influence of process factors on the crystal morphology of nanohydroxyapatite" in Table 1 of Lv Kuilong's paper No. 11. The specific preparation method of the antibacterial agent is as follows: 100ml of butyl titanate is taken at room temperature and slowly dripped into 350ml of anhydrous ethanol, then 0.1g of stearic acid is added, and vigorously stirred with a magnetic stirrer for 10min to mix evenly. , forming a yellow clear solution C; add 7g of hydroxyapatite, 40ml of glacial acetic acid, and 100ml of distilled water to another 350ml of anhydrous ethanol and stir at high speed to obtain solution D; add 5-10 drops of hydrochloric acid to adjust the pH to pH ≤ 3; in a room temperature water bath, under vigorous stirring, slowly add solution C to solution D at a rate of about 10ml / min; after the addition is complete, a light yellow solution is obtained. After continuous stirring for half an hour, heat in a 45°C water bath to obtain a white gel after 1 hour; dry the sol at 105°C to obtain titanium dioxide-modified hydroxyapatite with low water absorption;

[0059] Example 2: 5 parts of a nucleating agent and 3 parts of an antibacterial agent, the nucleating agent is a degradable polyethylene glycol-modified hyperbranched polyether ester with Mn=24000 g / mol, prepared according to Example 4 in CN 101235134 "Degradable polyethylene glycol-modified hyperbranched polyether ester and its preparation method"; the antibacterial agent is titanium dioxide-modified hydroxyapatite with low water absorption. Hydroxyapatite is a nano-scale powder, homemade, with an average particle size of 149nm. The preparation method is based on the samples in Table 2-3 of Liu Ying's doctoral thesis "Preparation, Characterization and Performance Research of Functional Nano-Hydroxyapatite" from Jilin University. The reaction temperature is 4°C, and the average particle size of the antibacterial agent is 200nm. The preparation method is as follows: 100ml of butyl titanate is taken at room temperature and slowly dripped into 350ml of anhydrous ethanol, and then 0.1g of stearic acid is added and vigorously stirred with a magnetic stirrer for 10min. Mix well to form a yellow clear solution C; 20g of hydroxyapatite, 40ml of glacial acetic acid and 100ml of distilled water are added to another 350ml of anhydrous ethanol and stirred at high speed to obtain solution D; 5-10 drops of hydrochloric acid are added to adjust the pH to ≤3; in a room temperature water bath, solution C is slowly dripped into solution D under vigorous stirring at a dripping rate of about 10ml / min; after the addition is completed, a light yellow solution is obtained, which is continuously stirred for half an hour and heated in a 45°C water bath to obtain a white gel after 1h. The sol was dried at 105°C to obtain titanium dioxide-modified hydroxyapatite with low water absorption;

[0060] Example 3: 3 parts of nucleating agent and 1 part of antibacterial agent, the nucleating agent is a degradable polyethylene glycol modified hyperbranched polyether ester, homemade, Mn = 14000g / mol, the preparation method is in accordance with Example 3 in CN 101235134 "Degradable polyethylene glycol modified hyperbranched polyether ester and its preparation method"; the antibacterial agent is low water absorption titanium dioxide modified hydroxyapatite, with an average particle size of 36.6nm, the preparation method is in accordance with the sample in Table 2-3 of Liu Ying's doctoral thesis "Preparation, Characterization and Performance Study of Functional Nanohydroxyapatite" of Jilin University, the reaction temperature is 95 ° C, and the preparation method is as follows: take 100ml of butyl titanate at room temperature, slowly drip it into 350ml of anhydrous ethanol, then add 0.1g of stearic acid, and use magnetic Stir vigorously with a power blender for 10 minutes to mix thoroughly, forming a yellow, clear solution C. Add 8.6g of hydroxyapatite, 40ml of glacial acetic acid, and 100ml of distilled water to another 350ml of anhydrous ethanol and stir at high speed to obtain solution D. Add 5-10 drops of hydrochloric acid to adjust the pH to ≤3. In a room temperature water bath, slowly drip solution C into solution D at a rate of approximately 10ml / min while vigorously stirring. After the addition is complete, a light yellow solution is obtained. After continuous stirring for half an hour, heat in a 45°C water bath to obtain a white gel after 1 hour. Dry the sol at 105°C to obtain titanium dioxide-modified hydroxyapatite with low water absorption.

[0061] Example 4: 4 parts of nucleating agent and 2 parts of antibacterial agent, the nucleating agent is a degradable polyethylene glycol modified hyperbranched polyether ester, Mn = 17000g / mol, the preparation method is in accordance with Example 2 in CN 101235134 "Degradable polyethylene glycol modified hyperbranched polyether ester and its preparation method"; the antibacterial agent is low water absorption titanium dioxide modified hydroxyapatite, with an average particle size of 60nm, the preparation method is in accordance with the sample in Table 3-9a of Liu Ying's doctoral thesis "Preparation, Characterization and Performance Study of Functional Nanohydroxyapatite" of Jilin University, the reaction temperature is 40 ° C, and the preparation method is as follows: 100ml of butyl titanate is taken at room temperature and slowly dripped into 350ml of anhydrous ethanol, then 0.1g of stearic acid is added, and vigorously stirred with a magnetic stirrer for 10min, and mixed. The mixture was stirred evenly to form a yellow clear solution C; 15.6 g of hydroxyapatite, 40 ml of glacial acetic acid, and 100 ml of distilled water were added to another 350 ml of anhydrous ethanol and stirred at high speed to obtain solution D; 5-10 drops of hydrochloric acid were added dropwise to adjust the pH to ≤ 3; in a room temperature water bath, solution C was slowly added dropwise to solution D at a rate of approximately 10 ml / min while vigorously stirring; after the addition was completed, a light yellow solution was obtained, which was stirred continuously for half an hour and then heated in a 45°C water bath to obtain a white gel after 1 hour; the sol was dried at 105°C to obtain titanium dioxide-modified hydroxyapatite with low water absorption;

[0062] S4, mixing raw material A and raw material B to prepare a modified PLA resin, wherein raw material A and raw material B are fed in equal proportions through the main feeding port and the second feeding port of the twin-screw extruder using a mass-type main feeder, and the prepared raw materials are sequentially blended and granulated, melt-plasticized, extruded into strips, cooled and pelletized, and dried in the twin-screw extruder to obtain a PLA resin with low water absorption, i.e., a modified PLA resin;

[0063] S5, melt-blowing the modified PLA resin to obtain a PLA melt-blown filter material, first pre-treating the PLA resin with low water absorption: drying it in a blast oven at a temperature of 80-100°C for 4-6 hours, then filtering the pre-treated PLA resin with low water absorption at 200-240°C, and then measuring it, extruding it from the spinneret holes on the spinneret at 220-250°C, and then stretching it at a hot air temperature of 230-260°C and a hot air pressure of 0.05-0.3 MPa, and then bonding it through a web to obtain a PLA melt-blown filter material with low water absorption.

[0064] Example 1: The selected treatment conditions are drying in a blast oven at 80°C for 6 hours, filtering at 200°C, extruding at 220°C, and stretching and bonding at 230°C and a hot air pressure of 0.05 MPa.

[0065] Example 2: The selected treatment conditions are drying in a blast oven at 100°C for 4 hours, filtering at 240°C, extruding at 250°C, and stretching and bonding at 260°C and a hot air pressure of 0.3 MPa.

[0066] Example 3: The selected treatment conditions are: drying in a blast oven at 85°C for 5 hours, filtering at 220°C, extruding at 230°C, and stretching and bonding at 240°C and a hot air pressure of 0.2 MPa.

[0067] Example 4: The selected treatment conditions are: drying in a blast oven at 90°C for 4.5 hours, filtering at 230°C, extrusion at 240°C, and stretching and bonding at 250°C and a hot air pressure of 0.25 MPa.

[0068] S6. The prepared PLA melt-blown filter material is subjected to an electret treatment to obtain a low-water-absorption PLA melt-blown filter material with further improved filtration efficiency. The electret treatment parameters include a gap of 1 to 5 mm between the low-water-absorption PLA melt-blown filter material and the electret electrode rod, a treatment voltage of 10,000 to 50,000 V, a current of 2 to 10 A, and an electret speed of 5 to 30 m / min.

[0069] At the same time, the PLA resin in Example 3 (55 parts of 4032D from Natureworks, USA and 45 parts of D-rotatory D0710 from Purapol, Netherlands) was used to prepare different filter materials for performance testing and comparison.

[0070] Comparative Example 3-1:

[0071] In Example 3, no toughening agent, compatibilizer, nucleating agent, or antibacterial agent was added.

[0072] Comparative Example 3-2:

[0073] In Example 3, no toughening agent was added.

[0074] Comparative Example 3-3:

[0075] In Example 3, the bio-based polycarbonate toughening agent was replaced with bisphenol A polycarbonate, Hainan Huasheng 081S, with an Mn of approximately 20,000 g / mol).

[0076] Comparative Example 3-4:

[0077] In Example 3, no compatibilizer was added.

[0078] Comparative Examples 3-5:

[0079] In Example 3, the compatibilizer is an epoxy group-containing compatibilizer, ethylene-acrylic acid-glycidyl methacrylate (EMG), manufactured by Arkema, AX8900.

[0080] Comparative Examples 3-6:

[0081] In Example 3, the compatibilizer is a maleic anhydride compatibilizer, maleic anhydride grafted polylactic acid (LMA), which is homemade and prepared according to Section 2.4 of Shan Zhengzheng's master's thesis "Study on the Structure and Properties of Polycarbonate / Polylactic Acid Blends" from East China University of Science and Technology.

[0082] At the same time, a comparative example was carried out based on Example 4, and different filter materials were prepared to conduct performance test comparisons:

[0083] Comparative Example 4-1:

[0084] In Example 4, no nucleating agent was added.

[0085] Comparative Example 4-2:

[0086] In Example 4, the nucleating agent used was a conventional polylactic acid hydrazide nucleating agent, and the low-odor PLA nucleating agent TMC-300 from Quansheng Group was used.

[0087] Comparative Example 4-3:

[0088] In Example 4, no antimicrobial agent was added.

[0089] Comparative Example 4-4:

[0090] In Example 4, the antibacterial agent uses quaternary phosphine-modified amino nanocellulose, and the preparation method is in accordance with Example 1 of "CN202210419463 A PLA / PBAT composite flame-retardant, antibacterial and degradable staple fiber and its preparation method".

[0091] Comparative Example 4-5:

[0092] On the basis of comparative example 4-3, electret treatment was further performed, and the gap between the low water absorption PLA melt-blown filter material and the electret electrode rod was 1 to 5 mm, the processing voltage was 50,000 V, the current intensity was 2 A, and the electret speed was 30 m / min, and no electret was required.

[0093] Comparative Examples 4-6:

[0094] On the basis of Example 4, electret treatment was further performed, and the gap between the PLA melt-blown filter material with low water absorption and the electret electrode rod was 3 mm, the processing voltage was 10000 V, the current intensity was 10 A, and the electret speed was 5 m / min.

[0095] The performance indicators of the low water absorption PLA melt-blown filter materials prepared in each embodiment and comparative example are as follows: Table 1 Performance comparison of Examples 1 to 4; Table 2 Performance comparison of Example 3 and Comparative Example 3-1 to Example 3-6; Table 3 Performance comparison of Example 4 and Comparative Example 4-1 to Example 4-6;

[0096]

[0097]

[0098] Table 1

[0099] As can be seen from Table 1, the low water absorption PLA melt-blown filter material prepared in the embodiment of the present invention not only has excellent mechanical strength, toughness, biodegradability and low water absorption, but also has good thermal stability, filtration efficiency, air flow resistance and air permeability.

[0100] When pure PLA material is used to make filter material (Comparative Example 3-1), toughness and heat resistance are very poor, water absorption is very high, and filtration efficiency also decreases significantly. This is because high-strength, high-toughness, low-water absorption PLA melt-blown filter material is. Although PLLA and PDLA are used in combination, PLDA can induce the formation of a stereostructured crystal structure, but the PLLA and PDLA molecular chains are arranged alternately, and the molecular chains fold to form stereostructured lamellae, and interspersed with each other to form many defects, and the crystallinity is not high, resulting in poor mechanical properties and heat resistance. Although PLA has a good low water absorption rate, it has a high water absorption rate. When balanced in the air, the particle filtration efficiency will drop significantly after moisture absorption. After being placed for a long time, water molecules will diffuse between the PLA polymer chains, thereby causing its volume expansion. In addition, PLA has poor weather resistance and UV resistance, so the storage time is too long, degradation occurs, the mechanical properties further decline, and the appearance gradually changes from white to pink.

[0101] Compared to pure PLA material (Comparative Example 3-1), when no toughening agent is added (Comparative Example 3-2), the mechanical strength, toughness, water absorption rate and heat resistance of the PLA substrate are not ideal, and the improvement of various properties by the compatibilizer, nucleating agent and antibacterial agent is very limited. The toughening agent of the present invention is isosorbide-type aliphatic polycarbonate. When the toughening agent is replaced with bisphenol A polycarbonate (Comparative Example 3-3), although the mechanical properties, heat resistance and water resistance of bisphenol A polycarbonate are very excellent, since bisphenol A polycarbonate is an aromatic compound, it has poor compatibility with aliphatic compound PLA and compatibilizer (a binary copolymer of lactide and trimethylene carbonate (TMC)). At the same time, since aromatic carbonic acid is not biodegradable, the resulting blend has less ideal toughening and heat resistance than aliphatic polycarbonate, with a biodegradation rate of less than 85% and a significantly increased half-life.

[0102]

[0103] Table 2

[0104] As can be seen from Table 2, when not adding compatibilizer (Comparative Examples 3-4).Polycarbonate and PLA resin are directly blended, and interfacial compatibility is relatively poor, and two-phase can be separated, and PC melt viscosity is relatively large, and processing temperature is high, and the processing technology difference with PLA increases, and PC is used alone to carry out toughening heat-resistant modification to PLA, can significantly improve the melt viscosity of PLA resin, reduce its melt index, cannot be applied to melt-blown material.And the processing interval of PLA and PC differs greatly, does not add suitable compatibilizer, and each performance index is all undesirable.And when adding traditional epoxy group-containing compatibilizer (Comparative Examples 3-5, EMG) and maleic anhydride compatibilizer (Comparative Examples 3-6, LMA), although mechanical property and thermotolerance all have certain improvement, but on the whole, all differ greatly from the effect of embodiments of the present invention 3, and non-biodegradable. This is because EMG is composed of three blocks of ethylene, acrylate, and glycidyl methacrylate, and PLA and PC contain terminal hydroxyl groups. The epoxy groups in EMG react with the terminal hydroxyl groups of PLA / PC, playing a certain role in reactive compatibilization. However, EMG also contains more than half of the polyethylene (PE) component. The structure and polarity of PE and PC are very different, and they are completely incompatible systems, so they have a certain destructive effect on the compatibilization effect. The reaction of maleic anhydride with terminal hydroxyl groups is a ring-opening process, forming an ester at one end and an acid at the other. Maleic anhydride reacts with the terminal hydroxyl groups of PLA or PC to play a compatibilizing role. However, for LMA to achieve better compatibility, the maleic anhydride grafting rate needs to exceed 5%. However, the molecular weight of the polylactic acid used in the synthesis of LMA needs to be the same as or slightly lower than that of the PLA matrix, so the grafting rate is difficult to increase. The compatibilizer used in the embodiment of the present invention is a binary copolymer of lactide and trimethylene carbonate (TMC), which is fully biodegradable. The lactide unit has the same or similar main chain structure as the PLA resin, and the trimethylene carbonate (TMC) unit is similar to the R structure in the toughening agent. The ratio and molecular weight of the binary components can be easily adjusted, so it can perfectly compatibilize the PLA resin and PC resin. The fiber surface in the filter material is very smooth. Figure 1 .

[0105]

[0106]

[0107] Table 3

[0108] When no nucleating agent is added, the mechanical properties and heat resistance of the filter material are poor, and the impact on other properties is not significant. This is because due to reasons such as entanglement of polymer molecular chains and high viscosity, PLLA and PDLA usually do not completely reach molecular-level mutual melting / dissolution. Therefore, the prepared mixture often contains separate PLLA or PDLA molecular chains and insufficiently combined PLLA and PDLA molecular chains. These molecular chains will preferentially form α crystals, resulting in unsatisfactory mechanical properties. Low molecular weight polymers make it difficult to ensure high mechanical strength of the material, and high molecular weight is not conducive to the formation of stereocrystals. When using traditional conventional polylactic acid hydrazide nucleating agents (Comparative Example 4-2), the mechanical properties and heat resistance are improved to a certain extent, but there is still a considerable gap compared to the embodiments of the present invention, because hydrazide nucleating agents can induce PLA to nucleate at higher temperatures. Usually, they self-assemble into bundled microcrystals through hydrogen bonds. These microcrystals act as nucleation sites and can induce PLA to quickly form a large number of spherulites or skewers and dendrites with special structures. But because nucleator itself is the system of non-biomass, therefore the addition and use of this type of nucleator destroy the biodegradable and recyclable characteristics of PLA to a certain extent.And the present invention adopts the left-handed PLA resin (PLLA) of suitable high molecular weight and the right-handed PLA resin (PDLA) of suitable low molecular weight composite (embodiment 4), under the effect of polymer nucleator degradable type polyethylene glycol modified hyperbranched polyether ester, blend very easily forms triclinic stereostructure, and melting point, heat resistance and mechanical strength are obviously improved.The crystal crystal that blend obtains is larger, and lattice is complete, on the one hand itself has excellent biodegradability, and can induce PLLA, PDLA blend to form the stereostructure of high crystallization temperature, on the other hand because of hyperbranched resin special structure, can penetrate into the blend molecular chain internal slip, be evenly dispersed, significantly reduce the molecular chain interaction force, drive molecular chain rapid motion, reduce processing temperature and system viscosity, improve melt index and lubricity.

[0109] When no antibacterial agent is added (Comparative Example 4-3), the mechanical properties decrease. When a traditional antibacterial agent is used (Comparative Example 4-4), the mechanical properties decrease more seriously. On the one hand, it is due to the compatibility of the antibacterial agent with the substrate, and on the other hand, it is because of the adverse effects of the small molecule additive on the mechanical strength of the substrate. The antibacterial agent used in the present invention is a nanocomposite powder with good physical reinforcement. When no antibacterial agent is used and an electret treatment is performed (Comparative Example 4-5), the various properties are basically unchanged and the filtration efficiency is not improved. This is because traditional antibacterial agents are not electrets. However, the low water absorption PLA melt-blown filter material of the present invention, after high-pressure polarization treatment (Comparative Example 4-6), not only has no effect on physical and mechanical properties, heat resistance, biodegradability and airflow resistance, but also further improves the particle filtration efficiency of the filter material (reaching KN95 or above). At the same time, after polarization treatment, one side of the fiber surface in the filter material is positively charged and the other side is negatively charged, which can have a strong adsorption effect on positively or negatively charged bacteria and particulate matter. In addition, the present invention uses titanium dioxide coated nano-hydroxyapatite as an antibacterial agent. The internal nano-hydroxyapatite has good biocompatibility, biodegradability and reinforcement. The surface-coated nano-titanium dioxide itself has stable chemical properties, is harmless to the human body and the environment, has natural ultraviolet shielding and photocatalysis, and photocatalysis occurs in the H2O and O2 system. The hydroxyl radicals produced can react with various bacteria and odorous bodies, and effectively sterilize and eliminate odors. During the use of the PLA material, the product surface forms a weakly acidic environment. Under light conditions, it can better coordinate with titanium dioxide to exert its broad-spectrum antibacterial function, inhibit and kill microorganisms, and has deodorizing, mildew-proof and disinfecting effects. In addition, PLA, titanium dioxide and hydroxyapatite have electret properties. After electret polarization treatment, polarized charges can be stably stored in the cavities of the core-shell structure formed by the internal hydroxyapatite and the external titanium dioxide, further improving the filtration efficiency and antibacterial properties and making it particularly suitable for application in the meltblown layer material of masks.

[0110] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A PLA melt-blown filter material with low water absorption, characterized in that : It includes the following components in parts by mass: 100 parts of PLA resin, 15-30 parts of a bio-based polycarbonate toughening agent with a number average molecular weight (Mn) of 15,000 to 35,000 g / mol, 4-10 parts of a compatibilizer, 2-5 parts of a nucleating agent, and 0.5-3 parts of an antibacterial agent; wherein the PLA resin includes 50-65 parts of a left-handed PLA resin with a number average molecular weight (Mn) of 45,000 to 120,000 g / mol and 35-50 parts of a bio-based polycarbonate toughening agent with a number average molecular weight (Mn) of 10,000 to 80,000 g / mol. l dextrorotatory PLA resin; the compatibilizer is a binary copolymer of lactide and trimethylene carbonate with a number average molecular weight (Mn) of 25,000 to 34,000 g / mol; the nucleating agent is a degradable polyethylene glycol-modified hyperbranched polyether ester with a number average molecular weight (Mn) of 7,500 to 24,000 g / mol; the antibacterial agent is titanium dioxide-modified hydroxyapatite with an average particle size of 100 nm to 200 nm; the bio-based polycarbonate toughening agent is a bio-based isosorbide-type polycarbonate toughening agent having the following structural formula: Wherein R is any one of dimethyl carbonate, diethyl carbonate, isomannide, n-butylene glycol, n-hexanediol, n-octanediol, n-decanediol, and tartaric acid derivatives, and m and n are the numbers of each monomer polymerized.

2. The PLA melt-blown filter material with low water absorption according to claim 1, characterized in that The mass ratio of the lactide to trimethylene carbonate is 20:80 to 70:

30.

3. A method for preparing a PLA melt-blown filter material with low water absorption, characterized in that : Using the component described in any one of claims 1 to 2, the steps are as follows: S1, drying and pre-treating the bio-based polycarbonate toughening agent as raw material A; S2, drying and pre-treating the PLA resin and the compatibilizer respectively; S3, mixing the dried pretreated PLA resin, the compatibilizer, the nucleating agent, and the antibacterial agent to form raw material B; S4, mixing raw material A and raw material B to prepare modified PLA resin; S5, melt-blowing the modified PLA resin to prepare a PLA melt-blown filter material.

4. The method for preparing the PLA melt-blown filter material with low water absorption according to claim 3, wherein : Also includes step S6, the prepared PLA melt-blown filter material is subjected to electret treatment.

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