A soft SMS non-woven fabric and preparation method thereof

Abstract

This application relates to the field of nonwoven fabric technology and specifically discloses a soft SMS nonwoven fabric and its preparation method. The soft SMS nonwoven fabric comprises a spunbond layer and a meltblown layer. The spunbond layer is composed, by weight, of 65-80 parts spunbond PP, 5-10 parts PE / PP copolymer, 2-4 parts PP-g-MAH, 4-6 parts dopamine-grafted hyperbranched polymer, and 7-11 parts mineralized nanocellulose. The soft SMS nonwoven fabric of this application can be used in medical protection, sanitary product materials, industrial filtration, and other fields. It has a comfortable feel and excellent softness.

Description

Technical Field

[0001] The present application relates to the technical field of nonwoven fabrics, and more particularly, to a soft SMS nonwoven fabric and a preparation method thereof. Background Art

[0002] SMS (Spunbond-Meltblown-Spunbond) non-woven fabric is a multi-layer nonwoven material composed of a spunbond layer (Spunbond) and a meltblown layer (Meltblown). Its composite structure provides mechanical support through the spunbond layer, and the meltblown layer achieves micron-level filtration. It combines excellent mechanical strength, high-efficiency filtration and good barrier properties, and is therefore widely used in medical protection, sanitary product materials, industrial filtration and other fields.

[0003] However, in actual applications, it is found that in order to ensure the mechanical properties and filtration performance of the material, existing SMS non-woven fabrics usually adopt a high-quantity meltblown layer and a strong consolidation process to increase the rigidity and hot rolling pressure of the fiber, which directly leads to the densification of the material structure, the decrease of fiber flexibility and fluffiness, and the irreversible sacrifice of the material softness. The finished products generally have the problems of hard feel and poor comfort, which limits their comfort when they are in direct contact with human skin. Especially in scenarios such as medical surgical gowns, protective clothing and baby care products, the defect of softness is more significant.

[0004] In response to the above-mentioned related technologies, the inventors discovered that existing methods for improving the softness of SMS nonwoven fabrics primarily employ methods such as adjusting fiber fineness and interlayer composite structures, such as using ultrafine fiber spunbond layers or reducing the weight of meltblown layers to reduce material rigidity, or by introducing chemical additives or post-treatment processes, such as adding softeners, lubricants, or performing surface softening treatments. However, these methods often improve the softness of SMS nonwoven fabrics at the expense of mechanical strength and filtration efficiency, making it difficult to meet the market's comprehensive requirements for high strength, high filtration efficiency, and long-lasting softness. Summary of the Invention

[0005] In order to improve the softness of SMS non-woven fabrics, enhance the comfort of use of SMS non-woven fabrics, and ensure the mechanical properties and filtration efficiency of SMS non-woven fabrics, the present application provides a soft SMS non-woven fabric and a preparation method thereof.

[0006] In the first aspect, the present application provides a soft SMS nonwoven fabric, which adopts the following technical solution:

[0007] A soft SMS non-woven fabric comprises a spunbond layer and a meltblown layer. The raw materials of the spunbond layer include, by weight, 65-80 parts of spunbond PP, 5-10 parts of PE / PP copolymer, 2-4 parts of PP-g-MAH, 4-6 parts of dopamine-grafted hyperbranched polymer and 7-11 parts of mineralized nanocellulose.

[0008] The inventors discovered that nanocellulose itself has a high aspect ratio and flexibility. When the mineralized nanocellulose is used to prepare the spunbond layer of a non-woven fabric, it can improve the agglomeration of nanocellulose and reduce the impact of the increased softness on the mechanical properties of the material. In addition, the mineralized layer on the surface of the mineralized nanocellulose makes the structure of the nanocellulose surface more fluffy, which helps to improve the air permeability of the non-woven fabric while maintaining the filtration efficiency of the non-woven fabric.

[0009] Hyperbranched polymers have a highly branched three-dimensional dendritic structure with less entanglement between molecular chains and low melt viscosity. They can act as molecular-level lubricants in the spunbond layer to reduce internal friction, significantly reduce the bending stiffness of the non-woven fabric, and increase the flexibility and fluffiness of the non-woven fabric.

[0010] Furthermore, the inventors introduced catechol groups into the hyperbranched polymer by dopamine grafting, giving the hyperbranched polymer a flexible skeleton and a polar lubricating layer. The dopamine-grafted hyperbranched polymer can act as a molecular bridge inside the spunbond layer, and enhance the compatibility between the mineralized nanocellulose and the spunbond PP matrix through the interaction between the catechol groups and the surface ions of the mineralized nanocellulose. At the same time, the thermal stability of the dopamine-grafted hyperbranched polyester and the mineralized nanocellulose is improved, and the structure can be kept stable during the subsequent melting process.

[0011] By adopting the above technical solution, compared with the traditional method of improving the softness of SMS non-woven fabrics, this application uses dopamine-grafted hyperbranched polymers and mineralized nanocellulose as soft functional components, which significantly improves the softness of the non-woven fabric while ensuring that the mechanical properties and filtration efficiency of the non-woven fabric are not affected.

[0012] Optionally, the dopamine-grafted hyperbranched polymer is a dopamine-grafted carboxyl-terminated hyperbranched polyester.

[0013] By adopting the above technical solution, the hyperbranched polyester has good compatibility with the spunbond layer matrix, and the terminal carboxyl group provides an active site for dopamine grafting. The dopamine-grafted terminal carboxyl hyperbranched polyester combines the adhesion of dopamine and the toughening effect of hyperbranched polyester, which helps to form a tighter network structure in the spunbond layer, thereby improving the softness of the non-woven fabric while ensuring filtration efficiency.

[0014] Optionally, the preparation method of the dopamine-grafted carboxyl-terminated hyperbranched polyester comprises the following steps:

[0015] S1: dissolving the carboxyl-terminated hyperbranched polyester in water, adding 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide under inert gas protection for stirring and activation, then adding dopamine hydrochloride, adjusting the pH to alkaline, and reacting in the dark to obtain a reaction solution;

[0016] S2: Add ether to the reaction solution for precipitation, collect the crude product after centrifugation, dialyze and dry it.

[0017] Optionally, the method for preparing the mineralized nanocellulose comprises the following steps:

[0018] The nanocellulose was dispersed in water and ultrasonicated to form a suspension;

[0019] The suspension is mixed with a CaCl2 solution, stirred, filtered, and washed. The washed nanocellulose is then dispersed in a Na2HPO4 solution, the pH is adjusted to alkaline, stirred, filtered, and washed. The above alternating deposition steps of CaCl2 and Na2HPO4 are repeated, and the mixture is filtered, washed, and dried to obtain the product.

[0020] By adopting the above technical solution, CaCl2 / Na2HPO4 are alternately deposited on the surface of nanocellulose to form a mineralized layer containing calcium ions and phosphate groups. Calcium phosphate nanoparticles are embedded in the nanocellulose network as rigid fillers, which can significantly improve the mechanical properties of nanocellulose and the dispersion uniformity of nanocellulose in the spunbond layer. The fluffiness is increased without significantly affecting the mechanical properties of the non-woven fabric, making the non-woven fabric softer and more comfortable.

[0021] Furthermore, the negatively charged phosphate groups can form chemical adsorption sites on the surface of nanocellulose, enhancing the interception efficiency of external bacteria, viruses and other biological particles through electrostatic attraction. In addition, the high specific surface area of ​​calcium phosphate effectively increases the physical interception ability of non-woven fabrics for pollutants such as proteins in droplets, which helps to improve the filtration efficiency of SMS non-woven fabrics.

[0022] Optionally, the nanocellulose is pretreated as follows:

[0023] NaIO4 is added to the nanocellulose suspension, and heated to react in the dark to obtain a hydroformylation nanocellulose suspension; the pH of the hydroformylation nanocellulose suspension is adjusted to alkaline, and ozone-containing gas is introduced for oxidation, and then centrifuged, washed and dried to obtain pretreated nanocellulose.

[0024] By adopting the above technical scheme, after formaldehyde and carboxylation treatment, on the one hand, the original hydrogen bonds between nanocellulose molecules can be destroyed during the oxidation process, effectively improving the dispersibility of nanocellulose, reducing the agglomeration of nanocellulose, forming a more fluffy network structure, and further improving the softness and air permeability of the material. On the other hand, the carboxylation treatment introduces carboxyl groups on the surface of nanocellulose, significantly increasing the Ca 2+ The chelation sites of cellulose promote the formation of a mineralized layer on the surface of nanocellulose.

[0025] Optionally, the melt index of the spunbond PP is 40-45 g / min, and the melt index of the meltblown PP is 1200-1500 g / min.

[0026] By adopting the above technical solution, the meltblown layer prepared with high melt index PP can form finer meltblown fibers, increase the number of fibers per unit area of ​​the non-woven fabric, form a denser filtration network, and maintain high filtration efficiency at a low grammage.

[0027] In a second aspect, the present application provides a method for preparing a soft SMS nonwoven fabric, which adopts the following technical solution:

[0028] A method for preparing a soft SMS nonwoven fabric comprises the following steps:

[0029] The raw materials for the spunbond layer are mixed according to a ratio, and the mixture is subjected to screw extrusion melting, spinning, cold air drawing, and web laying to obtain a spunbond layer; the raw materials for the meltblown layer are mixed according to a ratio, and the mixture is subjected to screw extrusion melting, spinning, hot air drawing, cooling, and web laying to obtain a meltblown layer; the meltblown layer is used as the middle layer, and spunbond layers are laid on both sides of the meltblown layer, and the mixture is obtained after hot pressing and bonding.

[0030] By adopting the above-mentioned technical solution, compared with the traditional strong consolidation process, the preparation method of this application improves the softness of the non-woven fabric in multiple dimensions through the effects of polymer material blending modification and nanomaterial reinforcement, and effectively improves the fluffiness and softness of the material while ensuring the interlayer bonding strength.

[0031] Optionally, when the screw extrusion melt is used to prepare the spunbond layer and the meltblown layer, the screw temperature is 210-230°C, and when the hot air drawing is used to prepare the meltblown layer, the hot air temperature is 230-250°C.

[0032] In summary, this application has the following beneficial effects:

[0033] 1. This application adopts PE / PP blends, dopamine-grafted hyperbranched polymers and mineralized nanocellulose as flexible components, and utilizes the highly branched three-dimensional dendritic structure of the hyperbranched polymer and the flexibility of nanocellulose to significantly improve the softness of the SMS non-woven fabric. The dopamine-grafted hyperbranched polymer plays the role of a molecular bridge in the spunbond layer. On the one hand, it is covalently linked to the anhydride group of PP-g-MAH and anchored in the PP matrix. On the other hand, it forms a hydrogen bond network with the calcium phosphate mineral layer on the surface of the mineralized nanocellulose, uniformly dispersing the mineralized nanocellulose in the PP matrix to form a uniform and dense network structure, thereby ensuring that the mechanical properties and filtration efficiency of the non-woven fabric are not affected.

[0034] 2. This application introduces inorganic fillers into SMS non-woven fabrics by alternately depositing CaCl2 and Na2HPO4 on the surface of nanocellulose to form an inorganic mineralized layer, thereby enhancing the dispersion of nanocellulose in the spunbond layer and reducing the agglomeration of nanocellulose. At the same time, it also promotes the dispersion uniformity of the inorganic filler in the spunbond layer and its compatibility with organic raw materials, effectively improving the softness of the SMS non-woven fabric while ensuring that the excellent mechanical properties of the non-woven fabric are not affected.

[0035] 3. The mineralized nanocellulose formed by the alternating deposition of CaCl2 and Na2HPO4 can enhance the interception efficiency of external bacteria, viruses and other biological particles through electrostatic adsorption. The high specific surface area of ​​calcium phosphate also enhances the physical interception effect of non-woven fabrics on external pollutant particles, which can improve the air permeability of non-woven fabrics while ensuring that the filtration efficiency of non-woven fabrics is not affected. DETAILED DESCRIPTION

[0036] The present application is further described in detail below with reference to the following examples and comparative examples.

[0037] raw material

[0038] Unless otherwise specified, the raw materials used in the preparation examples, examples and comparative examples in this application are all commercially available products, specifically:

[0039] Spunbond PP, melt index is 40-45g / min;

[0040] PE / PP copolymer, PE content is 14-16wt%, density is 0.9g / cm 3 ;

[0041] PP-g-MAH, selected from Exxon, PO1020;

[0042] Carboxyl-terminated hyperbranched polyester with a molecular weight of 6400 g / mol and 24 carboxyl groups / mol;

[0043] Dopamine hydrochloride, selected from Hefei Bomei Biotechnology Co., Ltd., DD5109;

[0044] Nanocellulose, with a diameter of 5-8 nm and an aspect ratio of (8-10):1;

[0045] Meltblown PP, the melt index of meltblown PP is 1200-1500g / min;

[0046] Polyethylene wax, selected from Honeywell, AC-6A.

[0047] Preparation Example 1.1 of Dopamine-Grafted Carboxyl-Terminated Hyperbranched Polyester

[0048] The preparation method of dopamine-grafted carboxyl-terminated hyperbranched polyester comprises the following steps:

[0049] S1: 5 g of carboxyl-terminated hyperbranched polyester was placed in a 250 mL three-necked flask, 100 mL of deionized water was added, nitrogen was introduced, and magnetic stirring was performed at 300 rpm until completely dissolved. Then, 3.6 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 2.1 g of N-hydroxysuccinimide were added, the pH was adjusted to 4.5-5, and the mixture was stirred and activated at 300 rpm for 1.5 h to obtain a blend;

[0050] S2: Add 7.2 g of dopamine hydrochloride to the blend, continue stirring, slowly adjust the pH to 8-9 with 1 mol / L NaOH solution, and react in the dark for 16 h to obtain a reaction solution;

[0051] S3: The reaction solution was added to 800 mL of pre-cooled ether under stirring for precipitation. The crude product was collected after centrifugation, dissolved in deionized water, and transferred to a dialysis bag for dialyzation for 48 h. The dialysis fluid was replaced every 8 h to remove unreacted small molecules, and then dried.

[0052] Preparation Examples 2.1-2.3 of Mineralized Nanocellulose

[0053] Preparation Example 2.1

[0054] The preparation method of mineralized nanocellulose comprises the following steps:

[0055] S1: Disperse nanocellulose in water and ultrasonically disperse for 30 min to form a 3% suspension;

[0056] S2: adding NaIO4 to the nanocellulose suspension under stirring, with a mass ratio of NaIO4 to nanocellulose in the suspension being 0.3:1, and heating to 55°C for 4 hours in the dark to obtain a hydroformylated nanocellulose suspension;

[0057] S3: The pH of the hydroformylated nanocellulose suspension obtained in step S2 was adjusted to 9-10 with a 1 mol / L NaOH solution, and then ozone-containing gas was introduced for oxidation under light-proof conditions, wherein the air flow rate and ozone inlet concentration were 1.8 NL / min and 2.5 wt%, respectively, and the ventilation time was 12 min. The suspension was then centrifuged, washed to neutrality, and dried to obtain pretreated nanocellulose;

[0058] S4: The pretreated nanocellulose was redispersed in water and ultrasonicated for 20 min to form a 3% suspension, which was then mixed with a 3% CaCl2 solution at a volume ratio of 1:1 and stirred for 20 min to allow CaCl2 to 2+ It is adsorbed on the surface of nanocellulose by electrostatic action, and then filtered and washed to remove the unadsorbed Ca2+ Then, the washed nanocellulose is dispersed in a 2% Na2HPO4 solution with the same volume as the CaCl2 solution, the pH is adjusted to 7.5-8.5, and after stirring for 25 minutes, it is filtered and washed. The above alternating deposition steps of CaCl2 and Na2HPO4 are repeated 5 times, and the nanocellulose is obtained after filtering, washing and drying.

[0059] Preparation Example 2.2

[0060] The preparation method of mineralized nanocellulose comprises the following steps:

[0061] S1: Disperse nanocellulose in water and ultrasonically disperse for 30 min to form a 4% suspension;

[0062] S2: adding NaIO4 to the nanocellulose suspension under stirring, with a mass ratio of NaIO4 to nanocellulose in the suspension being 0.35:1, and heating to 55°C for 4 hours in the dark to obtain a hydroformylated nanocellulose suspension;

[0063] S3: The pH of the hydroformylated nanocellulose suspension obtained in step S2 was adjusted to 9-10 with a 1 mol / L NaOH solution, and then ozone-containing gas was introduced for oxidation under light-proof conditions, wherein the air flow rate and ozone inlet concentration were 1.8 NL / min and 2.5 wt%, respectively, and the aeration time was 16 min. The suspension was then centrifuged, washed to neutrality, and dried to obtain pretreated nanocellulose;

[0064] S4: The pretreated nanocellulose was redispersed in water and ultrasonicated for 20 min to form a 4% suspension, which was then mixed with a 2% CaCl2 solution at a volume ratio of 1:1 and stirred for 20 min to allow the CaCl2 solution to 2+ It is adsorbed on the surface of nanocellulose by electrostatic action, and then filtered and washed to remove the unadsorbed Ca 2+ Then, the washed nanocellulose is dispersed in a 1% Na2HPO4 solution with the same volume as the CaCl2 solution, the pH is adjusted to 7.5-8.5, and after stirring for 25 minutes, it is filtered and washed. The above alternating deposition steps of CaCl2 and Na2HPO4 are repeated 4 times, and the nanocellulose is obtained after filtering, washing and drying.

[0065] Preparation Example 2.3

[0066] The preparation method of mineralized nanocellulose comprises the following steps:

[0067] S1: Disperse nanocellulose in water and ultrasonically disperse for 30 min to form a 5% suspension;

[0068] S2: adding NaIO4 to the nanocellulose suspension under stirring, with a mass ratio of NaIO4 to nanocellulose in the suspension being 0.4:1, and heating to 55°C for 4 hours in the dark to obtain a hydroformylated nanocellulose suspension;

[0069] S3: The pH of the hydroformylated nanocellulose suspension obtained in step S2 was adjusted to 9-10 with a 1 mol / L NaOH solution, and then ozone-containing gas was introduced for oxidation under light-proof conditions, wherein the air flow rate and ozone inlet concentration were 1.8 NL / min and 2.5 wt%, respectively, and the ventilation time was 15 min. The suspension was then centrifuged, washed to neutrality, and dried to obtain pretreated nanocellulose;

[0070] S4: The pretreated nanocellulose was redispersed in water and ultrasonicated for 20 min to form a 5% suspension, which was then mixed with a 4% CaCl2 solution at a volume ratio of 1:1 and stirred for 20 min to allow the CaCl2 solution to 2+ It is adsorbed on the surface of nanocellulose by electrostatic action, and then filtered and washed to remove the unadsorbed Ca 2+ Then, the washed nanocellulose is dispersed in a 3% Na2HPO4 solution with the same volume as the CaCl2 solution, the pH is adjusted to 7.5-8.5, and after stirring for 25 minutes, it is filtered and washed. The above alternating deposition steps of CaCl2 and Na2HPO4 are repeated 3 times, and the nanocellulose is obtained after filtering, washing and drying.

[0071] Preparation Example 2.4

[0072] The preparation method of mineralized nanocellulose comprises the following steps:

[0073] S1: Disperse nanocellulose in water and ultrasonically disperse for 30 min to form a 3% suspension;

[0074] S2: The suspension was mixed with 3% CaCl2 solution in a volume ratio of 1:1 and stirred for 20 min to make CaCl2 2+ It is adsorbed on the surface of nanocellulose by electrostatic action, and then filtered and washed to remove the unadsorbed Ca 2+ Then, the washed nanocellulose is dispersed in a 2% Na2HPO4 solution with the same volume as the CaCl2 solution, the pH is adjusted to 7.5-8.5, and after stirring for 25 minutes, it is filtered and washed. The above alternating deposition steps of CaCl2 and Na2HPO4 are repeated 5 times, and the nanocellulose is obtained after filtering, washing and drying. Example Example 1

[0075] A soft SMS nonwoven fabric comprises a spunbond layer and a meltblown layer, wherein the raw materials and amounts of the spunbond layer are shown in Table 1, wherein the dopamine-grafted hyperbranched polymer is a dopamine-grafted carboxyl-terminated hyperbranched polyester obtained by Preparation Example 1.1, and the mineralized nanocellulose is obtained by Preparation Example 2.1.

[0076] Table 1

[0077]

[0078] The method for preparing the soft SMS nonwoven fabric comprises the following steps:

[0079] S1: Spunbond PP, PE / PP copolymer, PP-g-MAH, dopamine-grafted hyperbranched polymer, mineralized nanocellulose, and antioxidant 1010 were mixed according to a certain ratio, extruded and melted using a screw extruder at 210°C, and then melt filtered and melt metered before being transported to a spinning box for extrusion at an extrusion pressure of 6.5 MPa. The mixture was cooled by air at 12°C, stretched, and laid to obtain a spunbond layer.

[0080] S2: 50 parts by weight of melt-blown PP and 1.5 parts by weight of polyethylene wax are mixed and melted at 210°C using a screw extruder. After melt filtration and melt metering, the mixture is transported to a spinning box and extruded at an extrusion pressure of 6.5 MPa. The mixture is stretched by hot air at 230°C and cooled by air at 20°C. The mixture is evenly spread on a high-speed mesh belt to form a melt-blown layer.

[0081] S3: With the meltblown layer as the middle layer, spunbond layers are laid on both sides of the meltblown layer, and hot pressing bonding treatment is performed. The hot rolling mill temperature is 145 ° C and the pressure is 50 KPa to obtain an SMS non-woven fabric with a gram weight of 30.7 gsm, of which the mass of the meltblown layer accounts for 10.5% of the entire SMS non-woven fabric. Example 2

[0082] A soft SMS nonwoven fabric is prepared, which differs from Example 1 in that the raw materials and amounts of the spunbond layer are as shown in Table 1. The specific preparation method comprises the following steps:

[0083] S1: Spunbond PP, PE / PP copolymer, PP-g-MAH, dopamine-grafted hyperbranched polymer, mineralized nanocellulose, and antioxidant 1010 were mixed according to a certain ratio, extruded and melted at 230°C using a screw extruder, and then melt filtered and metered before being transported to a spinning box for extrusion at an extrusion pressure of 6.5 MPa. The mixture was cooled by air at 12°C, stretched, and laid to obtain a spunbond layer.

[0084] S2: 50 parts by weight of melt-blown PP and 1.4 parts by weight of polyethylene wax are mixed and extruded into a melt at 230°C using a screw extruder. After melt filtration and melt metering, the mixture is transported to a spinning box and extruded at an extrusion pressure of 6.5 MPa. The mixture is stretched by hot air at 250°C and cooled by air at 20°C. The mixture is evenly spread on a high-speed mesh belt to form a melt-blown layer.

[0085] S3: With the meltblown layer as the middle layer, spunbond layers are laid on both sides of the meltblown layer, and hot pressing bonding treatment is performed. The hot rolling mill temperature is 140 ° C and the pressure is 55Kpa to obtain an SMS non-woven fabric with a gram weight of 29.9gsm, of which the mass of the meltblown layer accounts for 9.6% of the entire SMS non-woven fabric. Example 3

[0086] A soft SMS nonwoven fabric is prepared, which differs from Example 1 in that the raw materials and amounts of the spunbond layer are as shown in Table 1. The specific preparation method comprises the following steps:

[0087] S1: Spunbond PP, PE / PP copolymer, PP-g-MAH, dopamine-grafted hyperbranched polymer, mineralized nanocellulose, and antioxidant 1010 were mixed according to a ratio, extruded and melted using a screw extruder at 220°C, and then melt-filtered and melt-metered before being transported to a spinning box for extrusion at an extrusion pressure of 6.5 MPa. The mixture was cooled by air at 12°C, stretched, and laid to obtain a spunbond layer.

[0088] S2: 50 parts by weight of melt-blown PP and 1.7 parts by weight of polyethylene wax are mixed and extruded into a melt at 230°C using a screw extruder. After melt filtration and melt metering, the mixture is transported to a spinning box and extruded at an extrusion pressure of 6.5 MPa. The mixture is stretched by hot air at 240°C and cooled by air at 20°C. The mixture is evenly spread on a high-speed mesh belt to form a melt-blown layer.

[0089] S3: With the meltblown layer as the middle layer, spunbond layers are laid on both sides of the meltblown layer, and hot pressing bonding treatment is performed. The hot rolling mill temperature is 150 ° C and the pressure is 45Kpa to obtain an SMS non-woven fabric with a gram weight of 32.1gsm, of which the mass of the meltblown layer accounts for 9.2% of the entire SMS non-woven fabric. Example 4

[0090] A soft SMS nonwoven fabric is prepared, which differs from Example 1 in that the raw materials and amounts of the spunbond layer are as shown in Table 1. The specific preparation method comprises the following steps:

[0091] S1: Spunbond PP, PE / PP copolymer, PP-g-MAH, dopamine-grafted hyperbranched polymer, mineralized nanocellulose, and antioxidant 1010 were mixed according to a certain ratio, extruded and melted using a screw extruder at 210°C, and then melt filtered and melt metered before being transported to a spinning box for extrusion at an extrusion pressure of 6.5 MPa. The mixture was cooled by air at 12°C, stretched, and laid to obtain a spunbond layer.

[0092] S2: 50 parts by weight of melt-blown PP and 1.2 parts by weight of polyethylene wax are mixed and extruded into a melt at 220°C using a screw extruder. After melt filtration and melt metering, the mixture is transported to a spinning box and extruded at an extrusion pressure of 6.5 MPa. The mixture is stretched by hot air at 230°C and cooled by air at 20°C. The mixture is evenly spread on a high-speed mesh belt to form a melt-blown layer.

[0093] S3: With the meltblown layer as the middle layer, spunbond layers are laid on both sides of the meltblown layer, and hot pressing bonding treatment is performed. The hot rolling mill temperature is 145 ° C and the pressure is 50 KPa to obtain an SMS non-woven fabric with a gram weight of 33.2 gsm, of which the mass of the meltblown layer accounts for 10.4% of the entire SMS non-woven fabric. Example 5

[0094] A soft SMS nonwoven fabric is prepared, which differs from Example 1 in that the mineralized nanocellulose in the spunbond layer raw material is obtained from Preparation Example 2.2, and the other steps are the same as those in Example 1. Example 6

[0095] A soft SMS nonwoven fabric is prepared, which differs from Example 1 in that the mineralized nanocellulose in the spunbond layer raw material is obtained from Preparation Example 2.3, and the other steps are the same as those in Example 1. Example 7

[0096] A soft SMS nonwoven fabric is prepared, which differs from Example 1 in that the mineralized nanocellulose in the spunbond layer raw material is obtained from Preparation Example 2.4, and the other steps are the same as those in Example 1. Comparative Example

[0097] Comparative Example 1

[0098] A soft SMS nonwoven fabric is different from Example 1 in that the dopamine-grafted carboxyl-terminated hyperbranched polyester in the spunbond layer raw material is replaced with an equal mass of carboxyl-terminated hyperbranched polyester, and the other steps are the same as Example 1.

[0099] Comparative Example 2

[0100] A soft SMS nonwoven fabric is different from Example 1 in that no dopamine-grafted hyperbranched polymer is added, the dopamine-grafted carboxyl-terminated hyperbranched polyester in the spunbond layer raw material is replaced with spunbond PP of equal mass, and the other steps are the same as Example 1.

[0101] Comparative Example 3

[0102] A soft SMS nonwoven fabric is different from Example 1 in that the mineralized nanocellulose in the spunbond layer raw material is replaced by nanocellulose of equal mass that has not been mineralized, and the other steps are the same as Example 1.

[0103] Comparative Example 4

[0104] A soft SMS nonwoven fabric is different from Example 1 in that mineralized nanocellulose is not added, the mineralized nanocellulose in the spunbond layer raw material is replaced by spunbond PP of equal mass, and the other steps are the same as Example 1.

[0105] Comparative Example 5

[0106] A soft SMS nonwoven fabric, which differs from Example 1 in that mineralized nanocellulose and dopamine grafted hyperbranched polymer are not added, the mineralized nanocellulose and dopamine grafted hyperbranched polymer in the spunbond layer raw materials are replaced with spunbond PP of equal mass, and the other steps are the same as Example 1.

[0107] Performance testing

[0108] The following relevant performance test tests were performed on the soft SMS nonwoven fabrics obtained in Examples 1-7 and Comparative Examples 1-5. Each test was repeated three times, and the average value of the three test results was taken as the final result and the final result was recorded in Table 2.

[0109] 1. Breaking strength: Refer to the relevant provisions of GB / T 24218.3-2010 "Textiles - Test methods for nonwovens, Part 3: Determination of breaking strength and elongation at break (strip method)" to test the breaking strength of SMS nonwoven fabrics;

[0110] 2. Softness: Refer to the relevant provisions of GB / T 8942-2016 "Determination of softness of paper" to test the softness of SMS non-woven fabrics;

[0111] 3. Breathability: Refer to the relevant provisions of GB / T 5453 "Determination of air permeability of textile fabrics" and select 20cm 2 Test head, 200Pa pressure difference to test the air permeability of SMS non-woven fabric;

[0112] 4. Filtration efficiency: Refer to the YY0469-2011 medical surgical mask standard, tested at a NaCl aerosol flow rate of 28.3L / min, and the test instrument is the TSI 8130 Filtration Efficiency Tester.

[0113] Table 2

[0114]

[0115] According to the performance test results of Examples 1-6 and Comparative Example 5 in Table 2, it can be seen that the SMS non-woven fabric prepared in the present application by using PE / PP blends, dopamine-grafted hyperbranched polymers and mineralized nanocellulose as flexible components significantly improves the softness of the non-woven fabric without adversely affecting the mechanical properties of the non-woven fabric. Furthermore, the present application connects mineralized nanocellulose with other raw materials through hyperbranched polymers to form a more uniform and dense network structure inside the non-woven fabric, further improving the air permeability of the non-woven fabric while ensuring the filtration efficiency, which helps to improve the comfort of use of the non-woven fabric when used in medical protection, sanitary products and industrial filtration.

[0116] According to the performance test results of Example 1 and Comparative Examples 3-4, it can be seen that the mineralization treatment after oxidation of nanocellulose further improves the softness and fluffiness of nanocellulose, promotes the uniformity of dispersion of nanocellulose in the material matrix, effectively reduces the agglomeration of nanocellulose in the material matrix, and significantly improves the softness, mechanical properties and filtration efficiency of SMS non-woven fabrics.

[0117] In Comparative Example 3, the nanocellulose was added directly to the nonwoven fabric without undergoing mineralization treatment. While this effectively improved the nonwoven's softness, it significantly compromised its mechanical properties. Furthermore, the lack of mineralization reduced the uniformity of the nanocellulose's dispersion within the nonwoven fabric, potentially leading to localized agglomeration and the inability to form a uniform, dense network within the fabric, thus compromising the fabric's filtration performance.

[0118] In Example 7, the nanocellulose was directly mineralized without undergoing oxidative pretreatment. This reduced the nanocellulose's ability to adsorb inorganic particles. Under the same treatment conditions, the nanocellulose absorbed fewer inorganic particles, potentially leading to uneven surface mineralization and a less pronounced reinforcing effect of the inorganic particles within the nonwoven fabric. Furthermore, the softness of the nanocellulose that did not undergo oxidative modification was further improved compared to the nanocellulose that did undergo oxidative modification.

[0119] According to the performance test results of Example 1 and Comparative Examples 1-2, it can be seen that the use of dopamine-grafted end-carboxyl hyperbranched polyester not only helps to improve the softness of the non-woven fabric, but also can enhance the compatibility between the non-woven fabric raw materials through the role of its molecular bridge, thereby improving the mechanical properties and filtration performance of the non-woven fabric.

[0120] In Comparative Example 1, the carboxyl-terminated hyperbranched polyester was not grafted with dopamine, and the softness, mechanical properties and filtration efficiency of the non-woven fabric were all reduced. This is because the dopamine grafting method introduced catechol groups into the hyperbranched polymer, giving the hyperbranched polymer a flexible skeleton and a polar lubricating layer. The dopamine-grafted hyperbranched polymer can act as a molecular bridge inside the spunbond layer, and enhance the compatibility between the mineralized nanocellulose and the spunbond PP matrix through the interaction between the catechol groups and the surface ions of the mineralized nanocellulose, thereby promoting the formation of a more uniform and dense network structure inside the non-woven fabric, thereby ensuring that the filtration efficiency and mechanical properties of the non-woven fabric are stable and unaffected.

[0121] In Comparative Example 2, dopamine-grafted carboxyl-terminated hyperbranched polyester was not added, and only mineralized nanocellulose was added as a functional component to improve softness. The various properties of the non-woven fabric were adversely affected. This is because the hyperbranched polymer has a highly branched three-dimensional dendritic structure, with less entanglement between molecular chains and low melt viscosity. It can not only act as a molecular-level lubricant in the spunbond layer to reduce internal friction, significantly reduce the bending stiffness of the non-woven fabric, and increase the flexibility and fluffiness of the non-woven fabric, but also through the molecular bridge effect, on the one hand, it is covalently linked to the anhydride group of PP-g-MAH and anchored in the PP matrix. On the other hand, it forms a hydrogen bond network with the calcium phosphate mineral layer on the surface of the mineralized nanocellulose, thereby uniformly dispersing the mineralized nanocellulose in the PP matrix, thereby enhancing the compatibility between the mineralized nanocellulose and the spunbond PP matrix, and ensuring that the mechanical properties and filtration efficiency of the non-woven fabric are not affected.

[0122] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A soft SMS nonwoven fabric comprising a spunbond layer and a meltblown layer, characterized in that: The raw materials of the spunbond layer include 65-80 parts of spunbond PP, 5-10 parts of PE / PP copolymer, 2-4 parts of PP-g-MAH, 4-6 parts of dopamine-grafted hyperbranched polymer and 7-11 parts of mineralized nanocellulose in parts by weight; the dopamine-grafted hyperbranched polymer is a dopamine-grafted carboxyl-terminated hyperbranched polyester; The preparation method of the mineralized nanocellulose comprises the following steps: NaIO4 is added to a nanocellulose suspension, and the reaction is heated in the dark to obtain a hydroformylated nanocellulose suspension; the pH of the hydroformylated nanocellulose suspension is then adjusted to alkaline, a gas containing ozone is introduced for oxidation, and the suspension is then centrifuged, washed, and dried to obtain pretreated nanocellulose; the pretreated nanocellulose is dispersed in water and subjected to ultrasonic treatment to form a suspension; the suspension is mixed with a CaCl2 solution, stirred, filtered, and washed, and the washed nanocellulose is then dispersed in a Na2HPO4 solution, the pH is adjusted to alkaline, stirred, filtered, and washed, and the above-mentioned alternating deposition steps of CaCl2 and Na2HPO4 are repeated, and the suspension is filtered, washed, and dried to obtain the product.

2. The soft SMS nonwoven fabric according to claim 1, characterized in that: The preparation method of the dopamine-grafted carboxyl-terminated hyperbranched polyester comprises the following steps: S1: dissolving the carboxyl-terminated hyperbranched polyester in water, adding 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide under inert gas protection for stirring and activation, then adding dopamine hydrochloride, adjusting the pH to alkaline, and reacting in the dark to obtain a reaction solution; S2: Add ether to the reaction solution for precipitation, collect the crude product after centrifugation, dialyze and dry it.

3. The soft SMS nonwoven fabric according to claim 1, characterized in that: The raw material of the meltblown layer includes meltblown PP, the melt index of the spunbond PP is 40-45 g / min, and the melt index of the meltblown PP is 1200-1500 g / min.

4. The method for preparing a soft SMS nonwoven fabric according to any one of claims 1 to 3, characterized in that: The following steps are involved: The raw materials for the spunbond layer are mixed according to a ratio, and the mixture is subjected to screw extrusion melting, spinning, cold air drawing, and web laying to obtain a spunbond layer; the raw materials for the meltblown layer are mixed according to a ratio, and the mixture is subjected to screw extrusion melting, spinning, hot air drawing, cooling, and web laying to obtain a meltblown layer; the meltblown layer is used as the middle layer, and spunbond layers are laid on both sides of the meltblown layer, and the mixture is obtained after hot pressing and bonding.

5. The method for preparing a soft SMS nonwoven fabric according to claim 4, characterized in that: The screw temperature is 210-230° C. when the screw extrusion melt is used to prepare the spunbond layer and the meltblown layer, and the hot air temperature is 230-250° C. when the hot air drawing is used to prepare the meltblown layer.

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