A method for preparing flexible and degradable melt-blown filter material

Abstract

The present application provides a method for preparing a flexible and degradable melt-blown filter material, which belongs to the technical field of preparing compositions based on polymer compounds of polyesters obtained from hydroxy acids on the main chain. Synthesis of thermoplastic polyether ester copolymers: using tetrabutyl titanate as a catalyst, 1,4-dimethyl phthalate and diol as molten raw materials, and then adding polyethylene glycol and an antioxidant to obtain a thermoplastic polyether ester block copolymer, polylactic acid chips, thermoplastic polyether ester block copolymers and hydrophobic nanoparticles are melt-extruded to obtain a composite masterbatch; the composite masterbatch is melt-extruded, melt-blown, and drawn to obtain a micro-nanoscale melt-blown filter material, and finally a corona electret melt-blown filter material. The present application is applied to the processing of melt-blown filter materials, which have the advantages of being degradable and flexible.

Description

Technical Field

[0001] The present application relates to a method for preparing a flexible and degradable melt-blown filter material, and belongs to the technical field of preparing a composition based on a polymer compound of polyester obtained from a hydroxy acid on the main chain. Background Art

[0002] Masks are effective protective materials for isolating viruses, and wearing them when going out has become a common habit. Currently, used masks are non-degradable and require incineration, which seriously pollutes the environment. The core layer of the mask is composed of micro-nano meltblown filter material, replacing traditional non-degradable polypropylene resin with biodegradable polylactic acid (PL), meeting current social development needs. However, PLA resin is derived from lactic acid or lactide, a high molecular weight polymer with a high glass transition temperature and a low crystallization rate. While biodegradable, the resulting PLA meltblown filter material is brittle and lacks flexibility, requiring physical or chemical toughening to improve its mechanical properties.

[0003] "Preparation and Properties of PEG-Toughened Polylactic Acid Meltblown Nonwovens" (Dong Yujia et al., Journal of Basic Sciences of Textile Universities, 2022, 35(1), 14-23.) and CN105885374A both mentioned that polyethylene glycol (PEG) can effectively improve the flexibility of polylactic acid meltblown materials. The lower the relative molecular weight, the better the toughening effect. Although the addition of low-molecular-weight PEG significantly reduces the glass transition temperature of PLA, it also reduces the upper temperature limit of PLA and is prone to seepage, thus losing the toughening effect.

[0004] CN103003360A and “Effect of hot air temperature on the structure and properties of PP / TPU meltblown nonwovens” (Peng Mengna et al., Silk, 2018, 55(8), 35-40.) use thermoplastic polyurethane to toughen and improve the flexibility of PLA meltblown fabrics. However, polylactic acid and thermoplastic polyurethane are incompatible, and the toughening effect is limited, requiring the use of a compatibilizer. CN105442187A and “Structure and properties of PLA toughened with PCL of different molecular weights” (Meng Bing et al., Engineering Plastics Applications, 2016, 44(5), 107-111.) use biodegradable resin PCL to toughen PLA, but obvious phase separation occurs between PLA and PCL, which is not conducive to melt spinning processing. In the study "Study on the Effect of PLA-PCL-PLA on the Compatibility and Spinnability of PLA / PCL Blends for Meltblowing" (Master's thesis by Cao Yongmin, Zhejiang Sci-Tech University), PLA-PCL-PLA block copolymers were used as compatibilizers. However, these polymers have low glass transition temperatures and softness properties, resulting in poor stretchability under high-speed airflow, making it difficult to form meltblown fiber webs.

[0005] CN108440926A and CN103052672A directly graft polylactic acid (PLA) chains onto elastomer chains to enhance the flexibility of PLA. However, this grafting modification significantly increases the molecular weight and sharply reduces the melt index, hindering the preparation of PLA meltblown filter material.

[0006] “Preparation and properties of electret-plasticizer composite modified polylactic acid meltblown nonwoven materials” (Huang Haichao et al., Journal of Composite Materials, 2019, 36(3), 533-541) and CN103189131A. Adding inorganic nanoparticles can improve the strength, stiffness and toughness of the polymer, but it is related to the fact that they cannot be effectively dispersed in the PLA polymer, and the degree of effective toughening is low.

[0007] The above patent documents or journal documents propose preparation methods of toughened polylactic acid melt-blown filter materials from different perspectives. The general direction is to use low molecular weight PEG with good compatibility with PLA to toughen it, use polymer elastomers or degradable polymers with good toughness to toughen polylactic acid melt-blown filter materials, modify the polylactic acid molecular chain structure by elastic molecular chain grafting to improve the flexibility of polylactic acid filter materials, add nanoparticles to toughen and strengthen polylactic acid melt-blown filter materials, or a combination of these. The first technical problem is that low molecular weight PEG lowers the upper limit of the operating temperature of PLA and is easy to seep out of PLA and lose the toughening effect; the second technical problem is that the polymer elastomer is incompatible with polylactic acid, and the polymer glass transition temperature and softness properties of toughened PLA are low. Under high-speed airflow field, the drawing performance is poor, and it is more difficult to form a melt-blown fiber web; the third technical problem is that the polylactic acid molecular chain is grafted with elastomer, which affects the preparation of melt-blown filter material; the fourth technical problem is that although the addition of nanoparticles can improve the strength and toughness of PLA filter material to a certain extent, it is not easy to be effectively dispersed in the PLA polymer, and the effective toughening degree is low. Summary of the Invention

[0008] In view of this, the present application provides a method for preparing a flexible and degradable melt-blown filter material to improve the problems of brittle feel and poor flexibility of the polylactic acid melt-blown filter material.

[0009] Specifically, this application is implemented through the following solutions:

[0010] A method for preparing a flexible and degradable melt-blown filter material comprises the following steps:

[0011] (1) Synthesis of thermoplastic polyetherester copolymer: using tetrabutyl titanate (TBT) as a catalyst, 1,4-dimethyl phthalate (DMT) and diol are melt-condensed to obtain a hard segment, polyethylene glycol (PEG) and an antioxidant are then added, and the mixture is heated under stirring until an ester exchange reaction occurs, and the pressure is reduced to a set value and maintained for a period of time to obtain a thermoplastic polyetherester block copolymer. In the obtained thermoplastic polyetherester block copolymer, the mass fraction of the hard segment is maintained at 20-80% (preferably 40-80%), the melting point of the copolymer is 180-220°C, and the melt index is 20-50 g / min;

[0012] (2) Preparation of composite masterbatch: Polylactic acid (PLA) chips, thermoplastic polyetherester block copolymer and hydrophobic nanoparticles are uniformly mixed, melt-extruded, and then cooled and cut to obtain composite masterbatch;

[0013] (3) Preparation of polylactic acid melt-blown material: melt-extrusion, melt-blowing, and drawing of the composite masterbatch to obtain a micro-nano melt-blown filter material;

[0014] (4) Corona electret meltblown filter material.

[0015] The above scheme synthesizes thermoplastic polyether ester copolymers through hard segments and soft segments, and controls the rigidity and flexibility of the copolymer by controlling the type of hard segments and the molecular weight of the soft segments. At the same time, the soft segments can also serve as compatibilizers for hard segments, hydrophobic nanoparticles and polylactic acid. The polyether ester copolymers and hydrophobic nanoparticles synergistically toughen and reinforce the polylactic acid melt-blown filter material, and while improving the tensile strength of the filter material, its tensile elongation at break is increased, thereby improving the flexibility of the filter material and giving it good hand feel quality.

[0016] Furthermore, as a preference:

[0017] The diol is any one of 1,4-butanediol (BDO), 1,3-propylene glycol (PDO), and ethylene glycol (EG); the corresponding hard segment is polybutylene terephthalate PBT, polypropylene terephthalate PTT, and polyethylene terephthalate PTT; accordingly, the thermoplastic polyether ester block copolymer is PBT-PEG, PTT-PEG, and PET-PEG.

[0018] The hydrophobic nanoparticles are a mixture of any one or more of hydrophobic nano-silicon dioxide (SiO2), hydrophobic nano-titanium dioxide (TiO2), hydrophobic nano-calcium carbonate (CaCO3), and hydrophobic nano-silicon carbide (SiC), with an average nanometer particle size of 15 to 50 nm and a density of 0.1 to 0.2 g / m 3 .

[0019] In step (2), the mass ratio of the polylactic acid slices, the thermoplastic polyether ester copolymer and the hydrophobic nanoparticles is 92-95:2-8:0.2-0.5.

[0020] In step (2), the vacuum drying temperature is 80-100° C., and the drying time is 4-6 hours.

[0021] In step (2), the melting temperature is 200-240°C.

[0022] In step (3), the temperature of the three zones of the melt extruder is 170-240°C, and the extrusion rate of the metering pump is 60-100 cc.min. -1 .

[0023] In step (3), the hot air temperature on both sides of the drafting is 240-270°C, and the drafting fan speed is 1350-1450 r.min -1 .

[0024] In step (4), the negative electret voltage is 10 to 50 kV, and the electret distance is 2 to 8 cm.

[0025] The present application blends thermoplastic polyether ester copolymer and hydrophobic nanoparticles into polylactic acid slices to improve the problems of brittle feel and poor flexibility of polylactic acid melt-blown filter material, and develops thermoplastic polyether ester copolymer and hydrophobic nanoparticles synergistically toughened polylactic acid melt-blown filter material.

[0026] Compared with the previous toughened polylactic acid melt-blown filter material, the advantages of this application are:

[0027] (1) Synthetic thermoplastic polyetherester copolymer, hydrophobic nanoparticles and polylactic acid chips are mixed and granulated, and polylactic acid melt-blown filter material is prepared using a melt-blown process. The thermoplastic polyetherester copolymer is composed of polyether flexible segments and polyester hard segments. By synthesizing different segment lengths, different toughening effects on the polylactic acid melt-blown filter material are adjusted to solve the problem of easy brittleness of the filter material.

[0028] (2) Polyethylene glycol, as a flexible segment of the thermoplastic polyetherester copolymer, has good compatibility with polylactic acid molecular chains and hydrophobic nanoparticles, facilitating the effective dispersion of nanoparticles and hard segments in polylactic acid, and can serve as a compatibilizer for hard segment molecules, nanoparticles, and polylactic acid. Hydrophobic nanoparticles, as polylactic acid nucleating agents, can effectively promote the crystallization of polylactic acid and can be used as inorganic toughening and reinforcing agents. Furthermore, the thermoplastic polyetherester copolymer is a degradable material and does not affect the degradation properties of the matrix polylactic acid. DETAILED DESCRIPTION

[0029] The feasibility of this application is further verified by specific examples below. The examples listed are preferred solutions of this application. Therefore, this application is not limited to the examples. Anyone who imitates or changes the technical solution and concept of this application should fall within the scope of protection of this application.

[0030] 1. Raw materials:

[0031] PLA slices: melt-blown grade PLA, melt index 75g / 10min, melting point 165℃, glass transition temperature 60℃, relative molecular mass 2.5×10 5 , density 1.25g / m 3 .

[0032] Dimethyl 1,4-phthalate: molecular weight 194.18, purity 99%, Aladdin reagent.

[0033] 1,4-Butanediol, 1,3-Propanediol, Ethylene glycol: All are analytical grade, 98%, Aladdin reagent.

[0034] Tetrabutyl titanate: purity ≥99%, condensation catalyst, Aladdin reagent.

[0035] Polyethylene glycol: flexible chain segment, number average molecular weight 400-4000, analytical grade, Aladdin reagent.

[0036] Hydrophobic nanoparticles: hydrophobic nano-silicon dioxide (SiO2), hydrophobic nano-titanium dioxide (TiO2) or hydrophobic nano-calcium carbonate (CaCO3), hydrophobic nano-silicon carbide (SiC), with an average particle size of 15-50nm and a density of 0.1-0.2g / m 3 .

[0037] Antioxidants: hindered phenol antioxidants Irgafox 1010 or 1076, phosphite antioxidants Irgafos168, white powder, melting point <190°C, reagents from Ciba Fine Chemicals Co., Ltd., Switzerland.

[0038] 2. Test:

[0039] Samples were cut in the machine direction (MD) and cross direction (CD) according to GB / T 24218.3-2010. Sample width was 50 mm ± 0.5 mm, and the clamping distance was 200 mm. The samples were stretched at a constant extension rate of 100 mm / min until they broke. The breaking strength and elongation at break were recorded.

[0040] Example 1

[0041] The preparation process of the melt-blown filter material of this embodiment is as follows:

[0042] (1) DMT, 1,4-butanediol, and tetrabutyl titanate (catalyst, 0.2% wt DMT) were placed in a reactor, purged with nitrogen, heated to 190°C, and stirred for 2 hours to melt-polycondense to obtain PBT.

[0043] (2) PEG (Mn = 1000) was added to the reactor system, the mass ratio of PBT to PEG was 3:2 (i.e., the mass fraction of the hard segment was 60%), and an antioxidant (0.4% relative to the mass of the PBT / PEG system) was added. The mixture was slowly heated to a certain temperature (about 235°C) under continuous stirring to undergo an ester exchange reaction. The pressure in the reactor was then reduced to below 50 Pa and maintained for 6 hours to obtain a thermoplastic polyetherester block copolymer PBT-PEG.

[0044] (3) 93.7 parts by weight of polylactic acid chips were dried at 80°C for 8 h, and 6 parts by weight of PBT-PEG block copolymer and 0.3 parts by weight of hydrophobic nano-titanium dioxide (average particle size 30 nm, density 0.15 g / m) were added. 3 ) are dried at 80°C for 3h, and then the dried polylactic acid and the additives are crushed in a high-speed crusher and fully mixed in a high-speed stirring mixer at a temperature of 80°C. The mixed materials are then put into a twin-screw granulator for melt extrusion, and are cooled in a water bath and cut to obtain polylactic acid composite masterbatch.

[0045] (4) The polylactic acid composite masterbatch was vacuum dried at 80 °C for 2 h and then fed into the melt-blown equipment. The process parameters for preparing the melt-blown filter material are shown in Table 1.

[0046] (5) The modified polylactic acid melt-blown filter material was subjected to electret treatment using the positive and negative corona electret method. The electret negative electrode voltage was 30 kV and the electret distance was 4 cm. Flexible polylactic acid melt-blown filter material 1# was obtained.

[0047] The longitudinal breaking strength of filter material 1# is 24.08N / 5cm, and the transverse breaking strength is 17.97N / 5cm; the longitudinal breaking elongation is 18.61%, and the transverse breaking elongation is 13.86%.

[0048] Table 1: Meltblown filter material process parameter settings

[0049]

[0050] Example 2

[0051] The configuration of this embodiment is the same as that of embodiment 1, except that the molecular weight Mn of the added PEG is different.

[0052] Table 2: Effect of different PEG molecular weights on filter media strength and toughness

[0053]

[0054]

[0055] As can be seen from Table 2, as the molecular weight of PEG increases, the breaking strength decreases, while the elongation increases slightly; when the PEG molecular weight is controlled in the range of 1000 to 3000, the breaking strength and elongation at break are better.

[0056] Example 3

[0057] The configuration of this embodiment is the same as that of embodiment 1, except that the mass ratio of the hard segments is different.

[0058] Table 3: Effect of the hard segment mass ratio in thermoplastic polyetherester block copolymers on filter media

[0059]

[0060]

[0061] As can be seen from Table 3, as the amount of hard segments increases, the breaking strength increases significantly, while the breaking elongation decreases. When no hard segments are added (numbers 3-10), the breaking strength is lowest and the elongation is highest. The ideal mass ratio of hard segments in thermoplastic polyetherester block copolymers is 40-80%.

[0062] Example 4

[0063] The configuration of this embodiment is the same as that of embodiment 1, except that: in step (1), ethylene glycol is selected as the diol, and PET is obtained by melt polycondensation; in step (2), the Mn of PEG is 3000, and the mass ratio of PET to PEG is 7:3; in step (3), the raw material ratio is: 92.7 parts by mass of polylactic acid chips, 7 parts by mass of PET-PEG block copolymer, and 0.3 parts by mass of hydrophobic nano-titanium dioxide to obtain toughened polylactic acid melt-blown filter material 2#.

[0064] The longitudinal breaking strength of filter material 2# is 28.31N / 5cm, and the transverse breaking strength is 20.90N / 5cm; the longitudinal breaking elongation is 22.40%, and the transverse breaking elongation is 18.37%.

[0065] By comparing the above-mentioned Examples 1 to 4, it can be seen that the longitudinal and transverse breaking strengths of the melt-blown filter material prepared in this case are slightly increased, and the breaking elongation is significantly increased.

[0066] Comparative Example 1

[0067] The configuration of this comparative example is the same as that of Example 1, except that in step (2), the Mn of the added PEG is 1600; in step (3), the raw material ratio is: 93 parts of polylactic acid chips and 7 parts of PBT-PEG block copolymer. The resulting filter material is recorded as comparative 1#.

[0068] In comparison, the longitudinal breaking strength of 1# is 18.92N / 5cm, and the transverse breaking strength is 13.85N / 5cm; the longitudinal breaking elongation is 16.37%, and the transverse breaking elongation is 13.63%.

[0069] Comparing Example 2 (the solution corresponding to 2-2 in Table 2) with Comparative Example 1, when no hydrophobic nanoparticles were added, the breaking strength decreased and the elongation at break decreased slightly.

[0070] Comparative Example 2

[0071] In this comparative example, no block copolymer was added. 99.7 parts of polylactic acid chips and 0.3 parts of hydrophobic nano-silicon carbide were directly used as raw materials, and the same extrusion melting, melt blowing, and corona electret were performed as in Example 1 to prepare polylactic acid melt-blown filter material comparison 2#.

[0072] In comparison, the longitudinal breaking strength of 2# is 14.32N / 5cm, and the transverse breaking strength is 9.41N / 5cm; the longitudinal breaking elongation is 10.64%, and the transverse breaking elongation is 8.96%.

[0073] It can be seen from Comparative Example 2 that when only hydrophobic nanoparticles are added to the raw materials of the filter material without adding the thermoplastic polyetherester block copolymer, the breaking strength and elongation of the sample are both relatively low.

[0074] Comparative Example 3

[0075] In this comparative example, no additives were added. Polylactic acid chips were used directly as raw material, dried at 80°C for 2 hours, and then fed into a meltblown machine. The process parameters for preparing the meltblown filter material are shown in Table 1. The modified polylactic acid meltblown filter material was electret treated using positive and negative corona electrets, with a negative electret voltage of 30 kV and an electret distance of 4 cm. This yielded polylactic acid meltblown filter material comparison 3#.

[0076] In comparison, the longitudinal breaking strength of 3# is 12.72N / 5cm, and the transverse breaking strength is 8.76N / 5cm; the longitudinal breaking elongation is 10.45%, and the transverse breaking elongation is 8.81%.

[0077] Comparing Comparative Example 3 with Comparative Example 2, when the raw materials of the filter material are not added, the breaking strength decreases and the elongation at break does not change much, indicating that the hydrophobic nanoparticles can slightly improve the strength of the material, which also verifies the rationality of the above conclusions of Examples 1 to 4 and Comparative Examples 1 to 3.

Claims

1. A method for preparing a flexible and degradable melt-blown filter material, characterized in that: The following steps are involved: (1) Synthesis of thermoplastic polyether ester copolymer: Using tetrabutyl titanate as a catalyst, dimethyl 1,4-phthalate and diol are melt-condensed to obtain a hard segment, and polyethylene glycol and an antioxidant are added. The mixture is heated under stirring until an ester exchange reaction occurs. The pressure is reduced to a set value and maintained for a period of time to obtain a thermoplastic polyether ester block copolymer. The mass fraction of the hard segment in the obtained thermoplastic polyether ester block copolymer is maintained at 20-80%; (2) Preparation of composite masterbatch: polylactic acid chips, thermoplastic polyether ester block copolymer and hydrophobic nanoparticles are mixed evenly, vacuum dried, melt extruded, and then cooled and cut to obtain composite masterbatch; (3) Preparation of polylactic acid melt-blown material: melt extrusion, melt-blowing, and drawing of the composite masterbatch to obtain micro-nano melt-blown filter material; (4) Corona electret meltblown filter material.

2. The method for preparing a flexible and degradable melt-blown filter material according to claim 1, wherein: The diol is any one of 1,4-butanediol, 1,3-propylene glycol, and ethylene glycol.

3. The method for preparing a flexible and biodegradable melt-blown filter material according to claim 1, wherein: The mass fraction of the hard segment is maintained at 40~80%.

4. The method for preparing a flexible and degradable melt-blown filter material according to claim 1, wherein: The hydrophobic nanoparticles are a mixture of any one or more of hydrophobic nano-silicon dioxide, hydrophobic nano-titanium dioxide, hydrophobic nano-calcium carbonate, and hydrophobic nano-silicon carbide.

5. The method for preparing a flexible and degradable melt-blown filter material according to claim 1, wherein: In step (2), the mass ratio of the polylactic acid slices, the thermoplastic polyether ester copolymer and the hydrophobic nanoparticles is 92-95:2-8:0.2-0.

5.

6. The method for preparing a flexible and biodegradable melt-blown filter material according to claim 1, wherein: In step (2), the vacuum drying temperature is 80-100 °C and the drying time is 4-6 h.

7. The method for preparing a flexible and biodegradable melt-blown filter material according to claim 1, wherein: In step (2), the melting temperature is 200-240°C.

8. The method for preparing a flexible and biodegradable melt-blown filter material according to claim 1, wherein: In step (3), the temperature of the melt extruder is 170~240℃, and the extrusion rate of the metering pump is 60~100 cc.min -1 .

9. The method for preparing a flexible and biodegradable melt-blown filter material according to claim 1, wherein: In step (3), the hot air temperature on both sides of the drawing is 240~270℃, and the drawing fan speed is 1350~1450 r.min -1 .

10. The method for preparing a flexible and biodegradable melt-blown filter material according to claim 1, wherein: In step (4), the negative electret voltage is 10~50 kV and the electret distance is 2~8 cm.

Images