Fully biodegradable non-woven fabric obtained by blow molding and applied thereto to the manufacture of medical masks

Abstract

A fully biodegradable nonwoven fabric obtained by melt blow molding and its application in the manufacture of medical masks. This fully biodegradable nonwoven fabric is obtained by a melt blow molding process and its application in the manufacture of medical masks. The fully biodegradable nonwoven fabric is obtained through the following steps: (S1) preparation of a caprolactone-lactic acid copolymer; (S2) preparation of a copolymerized modified polylactic acid (PLA); and (S3) manufacture of a nonwoven fabric by blow molding. The PLA is modified multiple times in a gradient and then blended with other biodegradable materials to produce the nonwoven fabric by blow molding. The nonwoven fabric has excellent performance and can be completely degraded without causing environmental pollution.

Description

Title of the invention: FULLY DEGRADABLE NON-WOVEN FABRIC OBTAINED BY EXTRUSION BLOW MOLDING AND APPLICATION THEREOF TO THE MANUFACTURE OF MEDICAL MASKS Technical field

[0001] The present invention relates to non-woven fabrics, in particular a fully degradable non-woven fabric obtained by extrusion blow molding and an application thereof in the manufacture of medical masks. TECHNOLOGICAL BACKGROUND

[0002] Nonwoven fabrics are composed of directional or randomly distributed fibers, and are considered to be a new generation of environmentally friendly materials. They are breathable and thin, flexible, non-combustible, non-toxic and non-irritating, and have a low cost.

[0003] Extrusion blowing is a process for manufacturing a nonwoven fabric directly from a polymer, in which high-speed, high-temperature air blowing is used to gradually solidify a molten polymer net to further obtain ultrafine fibers. This process has been widely used in the manufacturing process of nonwoven fabrics.

[0004] Unfortunately, existing extrusion-blown nonwoven fabrics will cause environmental pollution due to the use of non-degradable polypropylene as a raw material. In this regard, several solutions have been proposed in the prior art for preparing an extrusion-blown nonwoven fabric from degradable materials. Chinese Patent Application No. 202011528027.X discloses "a degradable melt-blown nonwoven fabric for masks", but it only mentions the composition of the nonwoven fabric, and does not provide a specific method for processing the raw material into a nonwoven fabric using the melt-blown method. Therefore, whether the raw material can be processed into masks by a melt-blown method remains undetermined. SUMMARY

[0005] The objective of the present invention is to provide a fully degradable nonwoven fabric obtained by extrusion blow molding and an application thereof in the manufacture of medical masks, the nonwoven fabric being prepared from poly-lactic acid (PLA) which undergoes multiple gradient modifications and other materials degradable by the extrusion blow molding process. The nonwoven fabric according to the present invention has excellent performance, and can be completely degraded without causing environmental pollution.

[0006] The technical solutions of the present invention are described as follows.

[0007] The present invention firstly relates to a method for manufacturing a fully degradable non-woven fabric by extrusion-blowing, characterized in that it comprises the steps consisting of:

[0008] (SI) adding lactic acid (L-LA) and e-caprolactone (e-CL) into a reaction vessel to obtain a reaction system, the weight ratio of lactic acid (L-LA) to e-caprolactone (e-CL) in the reaction system being 1: (2 to 4);

[0009] adding a catalyst to the reaction system, followed by a reaction at 130 - 140°C under vacuum for 18-24 hours to obtain a crude copolymerization product, the catalyst representing 0.1 - 0.2% by weight of a total weight of the reaction system; and

[0010] purifying the crude copolymerization product to obtain a caprolactone-lactic acid random copolymer P(CL-co-LA);

[0011] (S2) drying polylactic acid (PLA);

[0012] mixing the dried PLA and P(CL-co-LA) uniformly, followed by melt mixing at a temperature of 180-190°C and a rotation speed of 50-100 rpm to obtain a mixture, the weight ratio of PLA to P(CL-co-LA) being (9-99):1, and the melt mixing being carried out for 5-10 min; and

[0013] subjecting the mixture to compression molding at 180-190°C and 8-10 MPa to finally obtain a copolymerized modified PLA; and

[0014] (S3) subjecting the copolymerized modified PLA, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), nano SiO2, a compatibilizer and a chain extender to a blend to obtain a melt blown blend, the weight ratio of PHBV copolymerized modified PLA to nano SiO2 to compatibilizer to chain extender being (80 - 95): (1 - 5): (0.1 -0.2): (0.001 - 0.005): (0.001 - 0.01);

[0015] introducing the melt blowing mixture into a screw extruder followed by melt extrusion and pelletizing at a temperature of 160-200°C to obtain mixture pellets; and

[0016] introducing the mixing pellets into the screw extruder, followed by melt extrusion and plasticization to obtain a melt extrusion product, and conveying the melt extrusion product into a die assembly, and ejecting the melt extrusion product through an orifice of a die of the assembly spinneret, followed by cooling and hot air stretching to form a meltblown nonwoven material on a collection device, and subjecting the meltblown nonwoven material to electret treatment to obtain the fully degradable nonwoven fabric.

[0017] According to a first aspect, the present invention relates to a fully degradable nonwoven fabric obtained by extrusion-blowing, the fully degradable nonwoven fabric being manufactured by the steps of:

[0018] (SI) adding lactic acid (L-LA) and e-caprolactone (e-CL) into a reaction vessel to obtain a reaction system, the weight ratio of lactic acid (L-LA) to e-caprolactone (e-CL) in the reaction system being 1:(2 to 4), preferably 1:3;

[0019] adding a catalyst to the reaction system followed by reaction at 130-140°C under vacuum for 18-24 hours to obtain a crude copolymerization product, the catalyst representing 0.1-0.2% by weight of the total weight of the reaction system, and the catalyst preferably comprising an N,N-donor zinc guanidine catalyst; and

[0020] purifying the crude copolymerization product, followed by drying at 40-50°C in a vacuum drying oven to obtain a random ca-prolactone-lactic acid copolymer P(CL-co-LA);

[0021] (S2) drying polylactic acid (PLA);

[0022] mixing a dried PLA and P(CL-co-LA) uniformly followed by melt mixing at a temperature of 180-190°C and a rotation speed of 50-100 rpm to obtain a mixture, the weight ratio of PLA to P(CL-co-LA) being (9-99):1, and the melt mixing being carried out for 5-10 min, preferably for 8 min; and

[0023] subjecting the mixture to compression molding at 180-190°C and 8-10 MPa to obtain a copolymerized modified PLA; and

[0024] (S3) subjecting the copolymerized modified PLA, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), nano SiO2, a compatibilizer and a chain extender to a blend to obtain a melt blown blend; the weight ratio of PHBV copolymerized modified PLA to nano SiO2 to compatibilizer to chain extender being (80 - 90): (1 - 3): (0.2 - 0.3): (0.005 - 0.01): (0.001 - 0.005); and the copolymerized modified PLA being sliced ​​and dried at 60°C for 24 - 48 hours to reduce the water content to less than 0.025% before blending;

[0025] introducing the melt blowing mixture into a screw extruder, followed by melt extrusion and pelletizing at 160-200°C to obtain mixture pellets; and

[0026] introducing the mixing pellets into the screw extruder, followed by melt extrusion and plasticization to obtain a melt extrusion product; accurately metering and conveying, by a metering pump, the melt extrusion product to a die assembly, and ejecting the melt extrusion product from an orifice of a die of the die assembly, followed by cooling and stretching using a high-speed and high-pressure hot air flow to form a melt-blown nonwoven material on a collection device (such as a receiving plate); and subjecting the melt-blown nonwoven material to electret treatment, cutting, winding and forming to obtain the fully degradable nonwoven fabric.

[0027] In a particular embodiment, in step (S1), the crude copolymerization product is purified by the steps consisting of:

[0028] (SI 1) subjecting the crude copolymerization product to ultrasonic treatment and / or microwave treatment, followed by precipitation with 90% (v / v) ethanol solution; and

[0029] (S 12) repeat step (SI 1) 1 - 2 times to obtain a purified copolymerization product.

[0030] In a particular embodiment, the ultrasonic treatment is carried out at an ultrasonic power of 200 - 300 W for 1 - 1.5 h; and the microwave treatment is carried out at a microwave power of 200 - 300 W for 0.5 - 1 h.

[0031] In a particular embodiment, in step (S3), the compatibilizer is selected from the group consisting of maleic anhydride, butyric anhydride, stearic anhydride, tannic acid and a combination thereof.

[0032] In a particular embodiment, the compatibilizer is a combination of maleic anhydride, butyric anhydride, stearic anhydride and tannic acid in a weight ratio of 1:2:2:1.

[0033] In a particular embodiment, in step (S3), the chain extender is a multifunctional epoxy chain extender (Joncryl® ADR chain extender).

[0034] In a particular embodiment, in step (S3), the distance between the die orifice of the die assembly and the collection device is 30 - 50 cm.

[0035] In a particular embodiment, the extrusion frequency of the die orifice is 1.5 Hz - 2.5 Hz.

[0036] In a particular embodiment, the temperature of the high-speed, high-pressure hot air flow is 240 - 260°C.

[0037] In a particular embodiment, in step (S2), the melt flow index of the PLA at 210°C is 20 and 40 g / 10 min.

[0038] In a particular embodiment, in step (S3), an electret material used in the electret treatment is obtained by electret corona; and the treatment by electret is performed at an electret voltage of 30 - 40 kV and an electrode distance of 2 - 4 cm for 1-2 min.

[0039] In a second aspect, the present invention also relates to an application of the fully degradable nonwoven fabric to the manufacture of a medical mask.

[0040] Compared with the prior art, the present invention has the following beneficial effects.

[0041] In the present invention, the raw materials of the nonwoven fabric are all fully degradable, so that the nonwoven fabric will not pollute the environment after use. In addition, the PLA raw material undergoes multiple gradient modifications before being used in the manufacture of the nonwoven fabric, and specifically, the PLA is first subjected to blending modification, then subjected to blending modification and chain extension modification to change the structure, thereby changing the properties of the PLA. The introduction of ultrasonic / microwave treatment and electret treatment during the modification process, as well as the optimization of various melt blowing parameters, significantly improve the performance of the nonwoven fabric. DETAILED DESCRIPTION OF EXAMPLES

[0042] In order to make the objectives, technical solutions and advantages of the present invention more clear, the latter will be described in more detail below with reference to the embodiments. Example 1

[0043] Provided herein is a fully degradable nonwoven fabric obtained by extrusion blow molding, which is manufactured by the following steps:

[0044] (SI) Preparation of a caprolactone-lactic acid random copolymer PlCL-co-LA).

[0045] Addition of lactic acid (L-LA) and e-caprolactone (e-CL) into a reaction vessel to obtain a reaction system, wherein the weight ratio of lactic acid (L-LA) to e-caprolactone (e-CL) in the reaction system is 1:(2 to 4), preferably 1:3.

[0046] Adding a catalyst to the reaction system followed by reacting at 130-140°C under vacuum for 18-24 hours to obtain a crude copolymerization product, the catalyst representing 0.1-0.2% by weight of the total weight of the reaction system, and the catalyst preferably comprising an N,N-donor guanidine zinc catalyst, which has the advantages of non-toxicity and a simple synthesis method. Compared with a common catalyst in polylactic acid production - stannous octoate, an N,N-donor catalyst Guanidine zinc has better activity to give ultra-high molecular weight polymer and faster catalytic reaction rate. The obtained polymer has better material stability and high molecular weight.

[0047] Purification of the crude copolymerization product followed by drying at 40-50°C, preferably at 45°C, in a vacuum drying oven to obtain the caprolactone-lactic acid random copolymer P(CL-co-LA). The step of purifying the crude copolymerization product comprises in particular the operations consisting of:

[0048] (SI 1) subjecting the crude copolymerization product to ultrasonic treatment and / or microwave treatment, followed by precipitation with 90% (v / v) ethanol solution; and

[0049] (S 12) repeat step (SI 1) 1 - 2 times to obtain a purified copolymerization product.

[0050] In a particular embodiment, the ultrasonic treatment is carried out at an ultrasonic power of 200 - 300 W for 1 - 1.5 h; and the microwave treatment is carried out at a microwave power of 200 - 300 W for 0.5 - 1 h. Therefore, the melt flowability of polylactic acid (PLA) is improved by the copolymerization modification of step (SI).

[0051] (S2) Preparation of copolymerized modified PLA.

[0052] Drying of polylactic acid (PLA), the melt flow index of PLA at 210°C being 20 - 40 g / 10 min.

[0053] Uniformly mixing the dried PLA and (P(CL-co-LA)) followed by melt mixing at a temperature of 180-190°C and a rotation speed of 50-100 rpm to obtain a mixture, wherein the weight ratio of PLA to P(CL-co-LA) is (9-99):1, and the melt mixing is carried out for 5-10 min.

[0054] The mixture is subjected to compression molding at 180 - 190 °C and 8 - 10 MPa to obtain the copolymerized modified PLA.

[0055] (S3) Preparation of a nonwoven fabric by extrusion-blowing.

[0056] An operation of subjecting copolymerized modified PLA, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), nano SiO2, a compatibilizer and a chain extender to blending to obtain a melt blowing blend; the weight ratio of copolymerized modified PLA to PHBV to nano SiO2 to compatibilizer to chain extender being (80 - 95): (1 - 5): (0.1 - 0.2): (0.001 - 0.005): (0.001 - 0.01); and the copolymerized modified PLA is sliced ​​and dried at 60°C for 24 - 48 hours to reduce the water content to less than 0.025% before blending. The compatibilizer is selected from the group consisting of maleic anhydride, butyric anhydride, stearic anhydride, acid tannic anhydride and a combination thereof. Preferably, the compatibilizer is a combination of maleic anhydride, butyric anhydride, stearic anhydride and tannic acid, in a weight ratio of 1:1:1:1. The chain extender is a multifunctional epoxy chain extender (Joncryl® ADR chain extender).

[0057] Introduction of the melt blowing mixture into a screw extruder followed by melt extrusion and pelletizing at 160-200°C to obtain mixture pellets.

[0058] Introducing the mixing pellets into the screw extruder, followed by melt extrusion and plasticization to obtain a melt extrusion product; accurately metering and conveying, by a metering pump, the melt extrusion product into a die assembly, and ejecting the melt extrusion product from an orifice of a die of the die assembly, followed by cooling and stretching using a high-speed and high-pressure hot air flow to form a melt-blown nonwoven material on a collection device (such as a receiving plate), and subjecting the melt-blown nonwoven material to electret treatment, cutting, winding and forming to obtain the fully degradable nonwoven fabric. The distance from the die orifice of the die assembly to the collection device is 30 - 50 cm.The extrusion frequency of the die orifice is 1.5 Hz -2.5 Hz. The temperature of the hot air flow is 240 - 260 °C. An electret material used in electret processing is obtained by corona electret and the electret processing is carried out at an electret voltage of 30 - 40 kV and an electrode distance of 2 - 4 cm for 1-2 min.

[0059] In step (S1) of this example, the crude copolymerization product may be subjected to ultrasonic treatment and / or microwave treatment for auxiliary purification, thereby increasing the yield of the copolymerized modified product, i.e., P(CL-co-LA). In the following, the auxiliary purification steps of the crude copolymerization product are optimized by adjusting different methods and conditions for purifying the crude copolymerization product. Specific settings are shown in Table 1.

[0060] Table 1: Influence of assisted purification conditions on the yield of P(CL-co-LA) Assisted purification conditions Average yield of P(CL-co-LA) (%) - 81% Ultrasonic treatment (300 W power, 1 h treatment time) 92% Microwave treatment (250 W power, 1 h treatment time) 85% Ultrasonic treatment + Microwave treatment 95%

[0061] Note: “-” means that the crude copolymerization product is not subjected to any auxiliary purification treatment, and that the crude copolymerization product is directly used as P(CL-co-LA).

[0062] It can be seen from Table 1 that when no auxiliary purification method is used, the average yield of the caprolactone-lactic acid random copolymer P(CL-co-LA) is only about 81%. Ultrasonic treatment or microwave treatment can improve the product yield to a certain extent, and the product yield is the highest after both treatments are carried out. Therefore, in step (SI 1), the crude copolymerization product is preferably subjected to the ultrasonic treatment and the microwave treatment, and the ultrasonic treatment is carried out at an ultrasonic power of 300 W for 1 h; and the microwave treatment is carried out at a microwave power of 250 W for 1 h.

[0063] In addition, this example also optimizes the weight ratio of PLA to P(CL-co-LA) in step (S2) (i.e., PLA / P(CL-co-LA)), which enables an effect of the weight ratio on the tensile strength and glass transition temperature of the copolymerized modified PLA to be discussed to obtain the copolymerized modified PLA with the best performance. Table 2 shows optimized settings. In this Table 2, a tensile strength test of the copolymerized modified PLA is carried out according to the tensile strength test method GB / T 1040-2006, and the pulling speed is 10 mm / min. For a test of the glass transition temperature of the copolymerized modified PLA, the dynamic mechanical analysis (DMA) test is adopted. The method is to adopt a film stretching mode, the frequency is 1 Hz, the heating rate is 3 °C / min, and the amplitude is 15 qm.

[0064] Table 2: Influence of the PLA / P(CL-co-LA) ratio on the copolymerized modified PLA PLA / P(CL-co-LA) Tensile strength (MPa) Glass transition temperature (°C) 100 / 0 61 81 99 / 1 73 65 97 / 3 66 72 95 / 5 60 73 90 / 10 51 81

[0065] It can be seen from Table 2 that, as the P(CL-co-LA) content increases, the tensile strength of the blend increases first and then decreases. When the weight fraction of P(CL-co-LA) is lower (1%), the P(CL-co-LA) is uniformly dispersed between the PLA molecular chains, occupying the spaces between the PLA molecular chains, and the molecular chains are more closely grouped. Therefore, the tensile strength of the copolymerized modified PLA is improved. When the amount of P(CL-co-LA) added continues to increase, the P(CL-co-LA) will fuse together, and plasticization will play a prominent role at that time. Therefore, the tensile strength of the copolymerized modified PLA decreases with the increase of P(CL-co-LA) addition. After testing the DMA copolymerized modified PLA, it is found that the glass transition temperature decreases first and then increases.When the weight ratio of copolymerized modified PLA to P(CL-co-LA) is 99:1, the glass transition temperature is the lowest, indicating that the addition of a small amount of P(CL-co-LA) can play an internal lubrication role and lower the glass transition temperature. This result is consistent with the stretching result. In summary, in step (S2), PLA and P(CL-co-LA) are uniformly mixed at a weight ratio of 99:1.

[0066] In one example, in step (S3), since the PLA molecule contains hydrophilic ester groups with a water content of 0.4%-0.6%, the molten PLA degrades very quickly in the presence of water, which further leads to a decrease in the molecular weight and a broadening of the molecular weight distribution of the PLA, resulting in a molecular weight and molecular weight distribution that are not suitable for spinning requirements. Furthermore, a polymer fluid channel is closed during a melt spinning process. When the polymer is melted by heat, the presence of moisture will not only affect the viscosity and fluid extrusion state of the polymer after melting, but may also form many tiny bubbles in the polymer.Bubbles can cause yarn breakage during a drawing process and have extremely adverse effects on the mechanical properties and fiber diameter of a product.

[0067] The moisture content, drying time and drying temperature of a wafer are the main factors affecting the thermal degradation of PLA. The higher the moisture content of the wafer, the greater the degree of degradation and the faster the degradation rate; the longer the drying time, the greater the degree of degradation; the higher the drying temperature, the faster the The faster the degradation, the greater the degree of degradation. Therefore, in step (S3), the copolymerized modified PLA must be dried before mixing to reduce the water content of the copolymerized modified PLA. Table 3 shows the optimal setting mode of slicing and drying conditions for the copolymerized modified PLA when the drying temperature is 60 °C.

[0068] Table 3: Influence of drying time at 60°C on the water content of the slice of copolymerized modified PLA Drying time (h) Average water content of the copolymerized modified PLA slice 12 0.135% 24 0.073% 36 0.057% 48 0.015%

[0069] Therefore, in step (S3), it is preferred to dry the copolymerized modified PLA wafer at 60°C for 48 hours to reduce the water content of the copolymerized modified PLA wafer to 0.025% while avoiding thermal degradation.

[0070] At the same time, in step (S3), the copolymerized modified PLA, PHBV (copolymer of 3-hydroxybutyrate and 3-hydroxyvalerate), nano SiO2, compatibilizer and chain extender are mixed to carry out mixing modification and chain extension modification. In the process for subsequently obtaining melt blown blends, this example also optimizes the proportions of the components to study how this affects the properties of the final fully degradable nonwoven fabric. Table 4 shows the effect of the weight ratio of the copolymerized modified PLA and PHBV on the performance of the fully degradable nonwoven fabric.

[0071] Table 4: Weight ratio of copolymerized modified PLA / PHBV / compatibilizer / chain extender / SiO2 Number PLA modified copolymerized PHBV Compatibilizer Chain extender Nano SiO2 1 100 - - - - 2 95 5 0.005 0.01 0.2 3 90 4 0.005 0.01 0.2 4 85 3 0.005 0.01 0.2 5 80 1 0.005 0.01 0.2

[0072] On this basis, a YG028-500 strength tester is used to test the mechanical properties of the finally obtained fully degradable nonwoven fabric. The results are shown in Table 5.

[0073] Table 5: Influence of the weight ratio of copolymerized modified PLA to PHBV on the mechanical properties of the fully degradable nonwoven fabric. Samples Longitudinal force (N) Transverse force (N) Longitudinal elongation (%) Transverse elongation (%) 1 12.04 7.61 15.08 17.40 2 11.78 7.54 27.16 32.78 3 11.54 7.53 45.44 47.57 4 11.24 7.14 51.27 49.48 5 10.24 6.98 67.15 61.28

[0074] In the process of compounding, extrusion, injection molding, spinning, etc., under the influence of heat, moisture, and impurities, the macromolecular chain of PLA will be broken, resulting in a decrease in the performance of the material, and active terminal groups (terminal carboxyl groups and terminal hydroxyl groups) are generated at the breaks of the molecular chain of PLA. The chain extender relies on its own active epoxy groups to produce coupling and branching reactions with the active terminal groups generated at the molecular chain breaks, thereby increasing the length of the molecular chain to obtain longer chain branches, and to increase the processing stability of PLA.

[0075] It can be seen from Table 5 that with the addition of PHBV, the transverse force and longitudinal force of the fully degradable nonwoven fabric decrease slightly, but the longitudinal elongation and transverse elongation increase greatly, indicating that the blending of PHBV and copolymerization modification PLA can give play to their performance advantages. At the same time, the addition of a small amount of nano SiO2 with good dispersibility can play a positive role in strengthening and improving the toughness. From the perspective of micromechanics, this can enable rigid nanoparticles to be dispersed in the polymer.When the polymer is subjected to an external force, a stress concentration effect is generated due to the presence of the rigid inorganic particles, which easily stimulates the surrounding polymer to produce microcracks (or splitting), absorbing some deformation work. At the same time, the polymer between the particles undergoes fining and produces a . plastic flow and plastic deformation, absorbing impact energy. In addition, the existence of rigid particles hinders and passivates the crack propagation of the polymer, which eventually stops and does not develop into destructive cracking, resulting in a strengthening and toughness-enhancing effect. In summary, in the melt blowing mixture of step (S3), the weight ratio of copolymerized modified PLA to PHBV is preferably 80:1.

[0076] In one example, under the condition that the copolymerized modified PLA: PHBV: nano SiO2: chain extender = 80: 1: 0.2: 0.01, the influence of different compatibilizer compositions on the mechanical properties of the fully degradable nonwoven fabric is studied, and the method for testing the mechanical properties of the fully degradable nonwoven fabric is the same as above, and the results are shown in Table 6.

[0077] Table 6: Influence of the composition of the compatibilizer on the mechanical properties of the fully degradable nonwoven fabric. Compatibilizer Type Longitudinal Strength (N) Transverse Strength (N) Longitudinal Elongation (%) Transverse Elongation (%) Maleic Anhydride 10.24 6.98 67.15 61.28 Maleic Anhydride: Butyric Anhydride = 1:1 10.78 7.12 68.43 62.14 Maleic Anhydride: Butyric Anhydride: Stearic Anhydride =1:1:1 11.98 7.43 68.75 63.26 Maleic Anhydride: Butyric Anhydride: Stearic Anhydride: 12.07 7.54 69.81 64.71 tannic acid = 1:1:1:1

[0078] Most compatibilizers contain polar groups, which can undergo an esterification reaction or form hydrogen bonds with the polar groups in a filler, thereby reducing the polarity and hygroscopicity of the filler. And the compatibilizer also contains non-polar segments having good compatibility with a polymer, the non-polar segments acting as a "bridge" to effectively bond the filler and the polymer together and improve the interfacial bonding performance of the filler and the polymer. It can be seen from Table 6 that an optimal compatibilizer ratio is, in a weight ratio, maleic anhydride: butyric anhydride: stearic anhydride: tannic acid =1:1:1:1. Under these conditions, the longitudinal force, transverse force, longitudinal elongation and transverse elongation of the fully degradable nonwoven fabric are all maximum.

[0079] Tables 4-6 analyze that the tensile strength and modulus of PHBV are low. PLA has the characteristics of high strength and high modulus, but due to its intrinsic brittleness, it has low elongation at break, low impact resistance and is extremely easy to bend and deform. Therefore, after blending PHBV and copolymerized modified PLA, the toughness of the nonwoven fabric can be improved while maintaining the degradation performance of a material. At the same time, in order to further increase a two-phase structure of the blends of the copolymerized modified PLA and PHBV, a compatibilizer (selected from a group consisting of maleic anhydride, butyric anhydride, stearic anhydride and tannic acid) is added to the PLA / PHBV blending system, so that the copolymerized modified PLA and PHBV can be better blended and enable their performance advantages to be played out.In addition, PLA is a crystalline polymer with some long branches in the molecular chain and a low degree of branching. Melted PLA is sensitive to temperature, and thermo-oxidative degradation or hydrolysis is likely to occur during processing to cause molecular chain breakage. All these factors lead to low melt viscosity and melt strength of PLA, poor melt viscoelasticity, and insufficient stress curing, which limits the processing technology of PLA. Therefore, on the one hand, the relative molecular weight of PLA can be increased by adding chain extenders.On the other hand, a long-chain branched structure is introduced into the PLA molecule to increase the melt strength of PLA, which in turn improves the processing properties of PLA, such as for thin sheet blowing, blow molding and . foaming.

[0080] Furthermore, provided that the copolymerized modified PLA: PHBV: nano SiO2: compatibilizer: chain extender = 80: 1: 0.2: 0.003: 0.01, this example also optimizes the parameters relating to melt blowing, including the receiving distance of the die orifice of the die assembly to the collection device (i.e., the "receiving distance"), the extrusion frequency of the die orifice (i.e., the "extrusion frequency"), the temperature of the hot air flow (i.e., the "hot air temperature"); Table 7 shows specific adjustment methods for investigating an influence on a performance of a melt blown product.

[0081] Table 7: Method for optimal adjustment of receiving distance, extrusion frequency and hot air temperature. Experimental parameters Receiving distance (cm) Hot air temperature (°C) Extrusion frequency (Hz) Receiving distance 30 250 2 40 250 2 50 250 2 Hot air temperature 40 240 2 40 250 2 40 260 2 Extrusion frequency 40 250 1.5 40 250 2 40 250 2.5

[0082] Based on Table 7, the influence of different receiving distances, hot air temperatures and extrusion frequencies on a diameter of a melt-blown fiber is studied.

[0083] Fiber diameter test: The fiber diameter size and distribution directly affect the pore size and pore size distribution of the nonwoven fabric, thereby affecting the filtration performance (filtration efficiency and filtration resistance) of the material. It is difficult to directly measure the fiber diameter. According to the invention, the Smile-view software is used to measure the fiber diameter taken by the scanning electron microscope of the nonwoven fabric to obtain the fiber diameter size and distribution. First, the fiber diameter is measured at 50 different positions for each sample, and an average value is taken to reduce the experimental error.

[0084] Influence of receiving distance on the diameter of a meltblown nonwoven fiber

[0085] Table 8 shows parameter adjustment methods and test results.

[0086] Table 8: Influence of different receiving distances on the diameter of meltblown nonwoven fiber. Receiving distance (cm) Average diameter (pm) CV value (%) 30 2.4 27.9 40 1.2 26.4 50 1.0 21.6

[0087] In step (S3), the nonwoven fiber obtained by the meltblowing method has a three-dimensional cross distribution. It can be seen from Table 8 that the longer the receiving distance, the smaller the fiber diameter. When the receiving distance increases from 30 cm to 50 cm, the average fiber diameter is reduced from 2.4 μm to 1.0 μm. The main reason is that when the receiving distance is small, the fiber cannot be effectively stretched, and sufficient cooling is not achieved, the degree of fiber entanglement increases, and a kinking phenomenon occurs.By increasing the receiving distance, the longer the fiber drawing time from the spinneret to the condensation drum, the weaker the bonding force between the fiber and the fiber, the more sufficient the fiber drawing and cooling, the more reduced the fiber fineness, and the more reduced the kinking phenomenon. After further consideration, in step (S3), the receiving distance from the spinneret orifice of the spinneret assembly to the collecting device is preferably 40-50 cm.

[0088] Effect of hot air temperature on meltblown nonwoven fiber diameter

[0089] Table 9 shows parameter setting methods and test results.

[0090] Table 9: Influence of different hot air temperatures on the diameter of the meltblown nonwoven fabric fiber. Hot air temperature (°C) Average diameter (pm) CV value (%) 240 2.5 26.9 250 1.2 26.4 260 1.9 28.9

[0091] In the melt blowing process, in order to avoid the rapid decrease in temperature of the fiber after its ejection from the die, so that the fiber could no longer be drawn, the hot air temperature is generally set to be slightly higher than the die temperature. It can be seen from Table 9 that the overall fiber diameter of the fiber is larger when the hot air temperature is 240°C, while the fiber diameter at 250°C and 260°C is relatively small, and it tends to decrease first and then increase. On the one hand, appropriately increasing the hot air temperature can prolong the cooling time of the fiber in the air, which is conducive to better drawing; on the other hand, as the temperature increases, the viscosity of the melt gradually decreases and the fluidity is better. It is easier to draw and thin, so the fiber diameter decreases accordingly.When the temperature of the hot air continues to increase, although the drawing effect reduces the fineness of the individual fiber, the molecular chain of the fiber becomes more active at this time, and the fiber is twisted during the drawing process, resulting in a slight increase in the average diameter of the fiber. After further consideration, in step (S3), the temperature of the hot air flow is preferably 250°C.

[0092] Effect of extrusion frequency on fiber diameter of meltblown nonwoven fabric

[0093] Table 10 shows parameter setting methods and test results.

[0094] Table 10: Influence of different extrusion frequencies on the diameter of the meltblown nonwoven fiber. Extrusion frequency (Hz) Average diameter (pm) CV value (%) 1.5 1.1 25.8 2 1.2 26.4 2.5 2.1 33.1

[0095] It can be seen from Table 10 that when the extrusion frequency is 2.5 Hz, the fiber diameter is larger and the distribution is uneven, mainly because the increase in the extrusion frequency increases the amount of fiber ejected from the die, and the drawing of the fiber during the drawing process is not uniform enough, resulting in serious differentiation in fiber fineness. When the extrusion frequency increases from 1.5 Hz to 2.5 Hz, the fiber diameter increases from 1.1 pm to 2.1 pm. The main reason is that when the extrusion frequency increases, the amount of melt stored in the extruder per unit time increases, and the melt is not completely melted in the extruder, resulting in an increase in the fiber diameter. After further consideration, in step (S3), the extrusion frequency of the die orifice is preferably 1.5 - 2 Hz.

[0096] Based on Table 7, the influence of different receiving distances, temperature The effect of hot air temperature and extrusion frequency on the air permeability, average pore size and thickness of fully degradable nonwoven fabric obtained by melt blowing process is investigated. The corresponding tests can be carried out according to GB / T 24218.15-2018 and GB / T 24218.2-2009.

[0097] Table 11 shows the influence of different receiving distances, hot air temperatures and extrusion frequencies on the air permeability and average pore diameter of the fully degradable nonwoven fabric obtained by the meltblowing process.

[0098] Table 11: Influence of receiving distance, hot air temperature and extrusion frequency on air permeability and average pore diameter of fully degradable nonwoven fabric. Experimental parameters Receiving distance (cm) Air permeability (mm / s) Average pore diameter (qm) Receiving distance (cm) 30 897.1 12.6 40 979.2 10.9 50 1184.7 10.4 Hot air temperature (°C) 240 911.2 15.4 250 979.2 10.9 260 1056.7 12.1 Extrusion frequency (Hz) 1.5 841.7 10.2 2 979.2 10.9 2.5 997.7 12.8

[0099] When using the nonwoven fabric to prepare disposable masks, it is necessary that the masks have good air permeability. It can be seen from Table 11 that, regardless of the conditions, the finally obtained nonwoven fabric has higher air permeability and smaller average pore size.

[0100] Table 12 shows the influence of different receiving distances, hot air temperatures and extrusion frequencies on the thickness of the fully degradable nonwoven fabric obtained by the melt blowing process.

[0101] Table 12: Influence of receiving distance, hot air temperature and extrusion frequency on the thickness of fully degradable nonwoven fabric. Experimental parameters Reception Distance Thickness Value CV (cm) (mm) (%) Receiving distance (cm) 30 1.04 3.78 40 1.29 1.24 50 1.91 2.91 Hot air temperature (°C) 240 1.28 3.24 250 1.29 1.24 260 1.30 3.78 Extrusion frequency (Hz) 1.5 1.27 2.27 2 1.29 1.24 2.5 1.42 2.28

[0102] It can be seen from Table 12 that the thickness of the nonwoven fabric increases with the increase of the receiving distance, which is mainly correlated with the fiber diameter and the bulkiness of the fiber web. When the temperature of the hot air increases, the thickness of the nonwoven fabric increases slightly. The reason is that when the temperature is low, the bonding between the fibers is strong, the fiber network structure is dense, the thickness is small, and when the temperature increases, the bonding between the fibers becomes weak, the structure of the fiber web is fluffy, and the thickness is large. When the extrusion frequency increases, the thickness of the nonwoven fabric increases. The reason is that the increase of the extrusion frequency makes the bonding between the fibers worse, the fiber web is fluffy, and the thickness increases.

[0103] In one example, the filtration efficiency of the nonwoven fabric can be improved by electret treatment. Therefore, this example also studies the influence of electret treatment conditions on the filtration performance of the nonwoven fabric. Three experimental groups are formed to prepare a fully degradable nonwoven fabric with reference to the melt blowing process. In this example, the difference is that in the melt blown mixtures corresponding to experimental group 1, experimental group 2 and experimental group 3, the ratios of copolymerized modified PLA: PHBV: nano SiO2: compatibilizer: chain extender are 80:1:0:0.003:0.01, 80:1:0.1:0.003:0.01, and 80:1:0.2:0.003:0.01, respectively.For each experimental group, in the manufacturing process of the fully degradable nonwoven fabric, in step (S3), a part of the melt-blown nonwoven material is taken for electret treatment, and a remaining part is not subjected to electret treatment. The electret treatment conditions are set as follows: electret voltage 40 kV, electrode distance 3 cm, electret time 1 min., the other remaining conditions are . the same.

[0104] The YG401 fabric induction electrostatic tester is used to test the electrostatic potential of the surface of the fully degradable nonwoven fabric finally obtained for each experimental group. During the test, the number of samples of the nonwoven fabric obtained without electret treatment and the nonwoven fabric obtained after electret treatment is 5, the distance between a probe and the test sample is 15 mm, the rotation speed of a turntable is 1500 rpm, and the test results are shown in Table 13.

[0105] Table 13: Filtration performance of fully degradable nonwoven fabric Group Resistance without electret (Pa) Filtration efficiency without electret (%) Resistance with electret (Pa) Filtration efficiency with electret (%) Resistance at 30 days (Pa) Efficiency at 30 days (%) Experimental group 1 18 38 18 92 18 90 Experimental group 2 19 41 19 91 19 91 Experimental group 3 20 40 20 93 20 92

[0106] It can be seen from Table 13 that after testing, the filtration efficiency of the nonwoven fabric obtained without electret treatment is only about 40%, while the filtration efficiency of the nonwoven fabric obtained after electret treatment can reach more than 90%. It can be seen that after electret treatment, the surface charge of the meltblown fibrous web increases, which significantly improves the filtration efficiency. At the same time, the test results show that the filtration performance of experimental group 3 is the best, which indicates that when the ratio of copolymerized modified PLA: PHBV: nano SiO2: compatibilizer: chain extender in the meltblown mixture is 80: 1: 0.2: 0.003: 0.01, the filtration performance of the nonwoven fabric is the best.

[0107] In one example, the electret-treated nonwoven fabric in each group is heated and immersed in water at room temperature, and the load resistance and filtration efficiency are not reduced, indicating that the filtration efficiency does not decrease over time.

[0108] After the tests, taking the electret-treated nonwoven in this example and Increasing the number of overlapping layers from 1 to 3, the particle filtration efficiency increased from 90% to 99.99%, which can fully meet the level 3 standard of a medical mask. When the number of overlapping layers is increased from 1 to 3, with a gas flow rate of 85 L / min, the airflow resistance is increased from 78.6 Pa to 247.1 Pa, which is in line with the inhalation resistance of medical masks, which should not exceed 343.2 Pa (35 mm H2O). From this result, it can be seen that the filtration efficiency can be increased by overlapping the number of layers of the nonwoven fabric obtained by electret treatment in this example. Example 2

[0109] This example also relates to an application of a fully degradable nonwoven fabric according to Example 1 in a manufacture of a medical mask, i.e., the fully degradable nonwoven fabric according to Example 1 is used to manufacture the medical mask, and a medical surgical mask may have several layers, of which an innermost layer and an outermost layer are made of a nonwoven fabric, with at least one layer of a nonwoven fabric obtained by the melt-blowing method according to Example 1 as a filter layer of the medium.

[0110] In one example, a performance evaluation of the medical mask is performed according to the following standards. [YES] 1. Filtration efficiency

[0112] When the gas flow rate is 85 L / min, the filtration efficiency of the medical mask for non-oily particles must meet the requirements of Table 14.

[0113] Table 14: Classification of filtration efficiency levels for non-oily particles by the medical mask Quality level Filtration efficiency (%) Level 1 >95 Level 2 >99 Level 3 >99.97

[0114] 2. Airflow resistance

[0115] When the gas flow rate is 85 L / min, the inhalation resistance of the medical mask must not exceed 343.2 Pa (35 mm H2O).

[0116] 3. Synthetic blood penetration

[0117] Spray 2 mL of synthetic blood onto the medical mask at a pressure of 10.7 kPa (80 mm Hg). There must be no penetration into the medical mask.

[0118] 4. Surface moisture resistance

[0119] The humidity level on an outer surface of the medical mask must not be lower than level 3 stipulated in GB / T 4745-1997, i.e. only a small unconnected area of ​​the surface is wet.

[0120] 5. Flame retardant performance

[0121] The materials used must not be flammable, and the continuous burning time must not exceed 5 seconds.

[0122] 6. Skin irritation

[0123] The primary irritation score of the medical mask material must not exceed 1.

[0124] 7. Waterproofing

[0125] The design of the medical mask must ensure a good seal, and the total adjustment factor of the medical mask must not be less than 100.

[0126] After testing, the performance of the medical mask in this example all meets the requirements.

[0127] In summary, the production materials of the nonwoven fabric according to the invention, such as PLA, PHBV, nano SiO2, compatibilizer, chain extender, etc., are all fully degradable materials, and the finally obtained nonwoven fabric can be fully degraded. The fully degradable nonwoven fabric is used to manufacture a medical consumable such as a medical mask, which will not pollute the environment after being used and discarded. At the same time, this application modifies the PLA several times in a gradient manner, that is, the PLA is first modified by copolymerization with e-caprolactone, and a resulting product is then blended with the PHBV, nano SiO2, compatibilizer, and chain extender for blending modification and chain extension modification to change the structure of the PLA polylactic acid, thereby changing the properties of the polymer.In addition, ultrasonic / microwave treatment and electret treatment are added during the modification process, and various melt-blowing parameters (such as receiving distance, hot air temperature, extrusion frequency, etc.) are optimized to improve the performance indicators of the finally obtained non-woven fabric, such as improving mechanical properties, increasing air permeability, fiber strength and filtration efficiency, so that it can meet the quality standards of medical masks and other consumables.

[0128] In the absence of conflict, examples and features of the examples of the present invention may be combined with each other.

[0129] The above examples are only preferred embodiments of the present invention and are not intended to limit it. It is understood that any modifications, substitutions and improvements made by those skilled in the art without departing from the spirit and scope of the present invention will fall within the scope thereof.

Claims

Claims

1. - A method of manufacturing a fully degradable nonwoven fabric by extrusion blow molding, characterized by the fact that it comprises the steps consisting of: (SI) adding lactic acid (L-LA) and e-caprolactone (e-CL) into a reaction vessel to obtain a reaction system, the weight ratio of lactic acid (L-LA) to e-caprolactone (e-CL) in the reaction system being 1: (2 to 4); adding a catalyst to the reaction system, followed by reaction at 130-140°C under vacuum for 18-24 hours to obtain a crude copolymerization product, the catalyst representing 0.1-0.2% by weight of a total weight of the reaction system; and purifying the crude copolymerization product to obtain a caprolactone-lactic acid random copolymer P(CL-co-LA); (S2) drying polylactic acid (PLA); mixing the dried PLA and P(CL-co-LA) uniformly, followed by melt mixing at a temperature of 180-190°C and a rotation speed of 50-100 rpm to obtain a mixture, the weight ratio of PLA to P(CL-co-LA) being (9-99):1, and the melt mixing being carried out for 5-10 min; and subjecting the mixture to compression molding at 180-190°C and 8-10 MPa to finally obtain a copolymerized modified PLA; and (S3) subjecting the copolymerized modified PLA, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), nano SiO2, a compatibilizer and a chain extender to blending to obtain a melt blowing mixture, the weight ratio of the copolymerized modified PLA to PHBV to nano SiO2 to the compatibilizer to the chain extender being (80-95): (1-5): (0.1-0.2): (0.001-0.005): (0.001-0.01); introducing the melt blowing mixture into a screw extruder followed by melt extrusion and pelletizing at a temperature of 160-200°C to obtain mixture pellets; and feeding the mixing pellets into the screw extruder, followed by melt extrusion and plasticization to obtain a melt extrusion product, and conveying the extrusion product in a melt state in a spinneret assembly, and ejecting the molten extrusion product through an orifice of a spinneret of the spinneret assembly, followed by cooling and hot air stretching to form a meltblown nonwoven material on a collection device, and subjecting the meltblown nonwoven material to electret treatment to obtain the fully degradable nonwoven fabric.

2. - A method according to claim 1, characterized in that, in step (S1), the crude copolymerization product is purified by the steps of: (S1 1) subjecting the crude copolymerization product to ultrasonic treatment and / or microwave treatment, followed by precipitation with a 90% (v / v) ethanol solution; and (S1 2) repeating step (S1 1) 1-2 times to obtain a purified copolymerization product.

3. - Method according to claim 2, characterized in that the ultrasonic treatment is carried out at an ultrasonic power of 200 - 300 W for 1 - 1.5 h; and the microwave treatment is carried out at a microwave power of 200 - 300 W for 0.5 - 1 h.

4. - Method according to claim 1, characterized in that, in step (S3), the compatibilizer is chosen from the group consisting of maleic anhydride, butyric anhydride, stearic anhydride, tannic acid and a combination thereof.

5. - Process according to claim 4, characterized in that the compatibilizer is a combination of maleic anhydride, butyric anhydride, stearic anhydride and tannic acid in a weight ratio of 1:1:1:

1.

6. - A method according to claim 1, characterized in that, in step (S3), the distance from the die orifice of the die assembly to the collection device is 30 - 50 cm; the extrusion frequency of the die orifice is 1.5 Hz - 2.5 Hz; and the temperature of the hot air flow is 240 - 260 °C.

7. - Method according to claim 1, characterized in that, in step (S2), the melt index of the PLA at 210 °C is 20 - 40 g / 10 min.

8. - A method according to claim 1, characterized in that, in step (S3), an electret material used in the electret treatment is obtained by electret corona; and the electret treatment is carried out at an electret voltage of 30 - 40 kV and an electrode distance of 2 - 4 cm for 1-2 min.

9. - Method according to claim 1, characterized in that, in step (S3), the copolymerized modified PLA is sliced and dried at 60°C for 24-48 h before mixing.

10. - Fully degradable nonwoven fabric obtained by the process according to any one of claims 1 to 9, for use in the manufacture of a medical mask.