Acid and alkali resistant non-woven fabric for filtration and preparation method thereof

Abstract

The invention relates to an acid and alkali resistant non-woven fabric for filtration and a preparation method thereof. The acid and alkali resistant non-woven fabric for filtration is prepared from polypropylene fibers and polyester composite fibers through a wet papermaking process, the polyester composite fiber is of a core-sheath structure, a core layer of the polyester composite fiber is a polyester fiber, and a sheath layer of the polyester composite fiber is an ethylene-trifluorochlor oethylene copolymer. The acid-resistant and alkali-resistant filter material is low in cost, simple in process and good in mechanical strength, has the characteristics of acid resistance and alkali resistance, and can be applied to filtration treatment in special environments such as strong acid or strong alkali.

Description

Technical Field

[0001] The invention relates to the technical field of preparation of filtering nonwoven fabrics, and in particular to an acid and alkali resistant filtering nonwoven fabric and a preparation method thereof. Background Art

[0002] The wet process for preparing non-woven fabrics for filtration is widely used in medicine, air filtration, water treatment and other fields because of its mature technology and strong versatility of equipment. The non-woven fabrics produced have uniform thickness, fine texture, high filtration accuracy and a variety of available raw materials.

[0003] The raw materials for current wet-laid non-woven fabrics are generally polyester fibers, polyethylene fibers, polypropylene fibers, and polytetrafluoroethylene fibers. Among them, 1) polyester fibers have high mechanical properties, good tensile strength, and air permeability, and are commonly used to produce non-woven fabrics for filtration. However, they are not acid-resistant. Under strong alkaline conditions, the ester groups of polyester fibers are easily hydrolyzed, destroying the crystal structure of the polyester fibers. 2) Polyethylene fibers have good chemical stability and tensile strength, but are not resistant to high temperatures and have a low melting point, making processing difficult and costly. 3) Polypropylene fibers have a non-polar chemical structure. According to the principle of like dissolves like, polar acids and bases do not react with polypropylene. Therefore, polypropylene has a certain chemical stability in acidic or alkaline solutions and has good acid and alkali resistance. However, compared with polyester fibers, it also has a low melting point and poor mechanical strength, making it unsuitable for use in wet-laid non-woven fabrics for filtration. 3) Although polytetrafluoroethylene fibers have excellent acid and alkali resistance, their production process is complex and the material cost is extremely high, limiting their application in non-woven fabrics for filtration.

[0004] Therefore, the above raw materials are not suitable for special applications that are resistant to acid and alkali, such as use in wastewater treatment and other environments. Therefore, it is extremely important to develop non-woven fabrics for wet filtration that are low in cost, simple in process, have good mechanical strength, and are resistant to acid and alkali, and their preparation methods. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide an acid- and alkali-resistant non-woven fabric for filtration and a preparation method thereof, which has low cost, simple process, good mechanical strength, and acid and alkali resistance, and can be used for filtration treatment in special environments such as strong acid or strong alkali.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] The invention discloses an acid- and alkali-resistant nonwoven fabric for filtering, which is prepared from polypropylene fiber and polyester composite fiber by a wet papermaking process; the polyester composite fiber has a core-sheath structure, wherein the core layer is polyester fiber and the sheath layer is ethylene-chlorotrifluoroethylene copolymer, and an adhesive layer is provided between the core layer and the sheath layer.

[0008] As a further technical solution, the mass ratio of the polypropylene fiber to the polyester composite fiber is 2.7-3.3:6.5-7.3.

[0009] As a further technical solution, the method for preparing the polyester composite fiber comprises the following steps:

[0010] Step (1), preparation of a binder: adding a boric acid crosslinker to deionized water, stirring and dissolving to prepare a boric acid aqueous solution; adding polyvinyl alcohol to deionized water, stirring and dissolving at 80 degrees Celsius to prepare a polyvinyl alcohol aqueous solution; then adding the boric acid aqueous solution to the polyvinyl alcohol aqueous solution while stirring, stirring and reacting at 80-100 degrees Celsius for 35 minutes, then adding montmorillonite and an emulsifier thereto, and high-pressure homogenizing for 90 minutes to obtain a binder solution;

[0011] Step (2) Surface pretreatment of the polyester fiber: the polyester fiber is sequentially immersed in a silane coupling agent solution and a binder solution (the polyester fiber is directly immersed in the binder solution without drying after being taken out of the silane coupling agent solution), taken out, and dried at 80 degrees Celsius to obtain the preliminarily treated polyester fiber for later use;

[0012] Step (3), electrostatic spraying: using electrostatic spraying technology to spray ethylene-chlorotrifluoroethylene powder onto the surface of the polyester fiber coated with the surface pretreatment;

[0013] Step (4), baking and cooling and drying: baking the polyester fiber with ethylene-chlorotrifluoroethylene sprayed on the surface, cooling to obtain the ethylene-chlorotrifluoroethylene coating layer, and then adjusting the fiber length to obtain a polyester composite fiber;

[0014] As a further technical solution, in step (1), the mass percentage of each raw material of the binder is:

[0015]

[0016] As a further technical solution, in step (2), the silane coupling agent is octadecyltrimethoxysilane,

[0017] As a further technical solution, the mass concentration of the silane coupling agent solution is 0.5-1.5%.

[0018] As a further technical solution, in step (2), the polyester fiber is immersed in the silane coupling agent solution for 15-25 seconds, and in the binder solution for 50-70 seconds.

[0019] As a further technical solution, in step (3), the ethylene-chlorotrifluoroethylene copolymer powder is further crushed by a micronized powder grinder before spraying, and sieved by a 100-mesh screen;

[0020] As a further technical solution, the spray thickness of ethylene-chlorotrifluoroethylene is 2-5 microns;

[0021] As a further technical solution, in step (4), the temperature of the baking treatment is 200 degrees Celsius and the time is 30-60 minutes; the fineness of the polyester composite fiber is 0.5-0.8 dtex.

[0022] A method for preparing an acid- and alkali-resistant nonwoven fabric for filtering comprises the following steps:

[0023] Step 1: Add polyester composite fiber, polypropylene fiber, defoaming agent, and PEO aqueous solution into deionized water, and stir ultrasonically for 60 minutes until uniformly dispersed to obtain fiber slurry;

[0024] Step 2: The fiber slurry is fed through a wet paper machine to form the nonwoven fabric, and excess moisture is removed from the nonwoven fabric by roller pressing and drying at 103°C to obtain a preliminary nonwoven composite fiber layer;

[0025] Step 3: The preliminary non-woven composite fiber layer is hot-pressed by a hard pressing roller and a soft pressing roller in sequence, so that the polypropylene fibers are melted and then the fibers are thermally bonded into a whole to obtain an acid and alkali resistant non-woven fabric.

[0026] As a further technical solution, in step 1, the fineness of the polypropylene fiber is 1.2-1.7 dtex (preferably 1.5±0.2 dtex); the concentration of the PEO aqueous solution is 0.02-0.03% (preferably 0.025%);

[0027] As a further technical solution, in step 3, the temperature of the hard pressing roller is 182°C, and the temperature of the soft pressing roller is 75°C.

[0028] The defoamer is a modified polyether defoamer.

[0029] Compared with the prior art, the technical effects of the present invention are:

[0030] 1. The present invention uses ethylene-chlorotrifluoroethylene copolymer to coat and modify polyester fibers to prepare polyester composite fibers, which are then blended with polypropylene fibers to prepare acid- and alkali-resistant nonwoven fabrics for filtration. While retaining the excellent properties of the polyester fiber nonwoven fabric, the acid and alkali resistance of the nonwoven fabric is improved, and the nonwoven fabric can be used for filtration operations in extreme acid or alkaline environments.

[0031] 2. In the preparation process of the polyester composite fiber, the present invention selects polyvinyl alcohol adhesive as the middle layer and uses a silane coupling agent to surface treat the polyester fiber, thereby improving the bonding strength between the ethylene-chlorotrifluoroethylene copolymer sheath layer and the polyester fiber and avoiding the problem of its falling off.

[0032] 3. Since the curing requirements of ethylene-chlorotrifluoroethylene copolymer are very high, and polyvinyl alcohol binder is not resistant to high temperatures, it will become brittle or even decompose at high temperatures. Therefore, in order to improve the heat resistance of the polyvinyl alcohol binder, the present invention also adds montmorillonite to the polyvinyl alcohol binder to prevent the cross-linked polyvinyl alcohol from changing its properties under the high temperature of baking and wet papermaking, which may affect the adhesion strength of the ethylene-chlorotrifluoroethylene copolymer. DETAILED DESCRIPTION

[0033] In the present invention,

[0034] Polyester fiber: melting point 245-260°C, fineness 0.3 dtex ± 0.1; purchased from Zibo Jinkeli Special Fiber Co., Ltd.

[0035] High melting point modified polypropylene fiber: melting point 165-180 °C, fineness 0.5 dtex ± 0.1, purchased from Zhejiang Yijiahui Industrial Co., Ltd.

[0036] Polypropylene fiber: melting point 120-130°C, fineness 1.5 dtex ± 0.2, purchased from Zhejiang Yijiahui Industrial Co., Ltd.

[0037] Ethylene-chlorotrifluoroethylene copolymer powder: melting point 235-245°C, purchased from Sinochem Blue Sky Group Co., Ltd.

[0038] Unless otherwise specified, the materials used in the present invention are commercially available.

[0039] The present invention is further described in detail below with reference to the embodiments.

[0040] Example 1

[0041] A method for preparing an acid- and alkali-resistant nonwoven fabric for filtration comprises the following steps:

[0042] Step 1: Preparation of polyester composite fiber:

[0043] Step (1), raw material pretreatment: the montmorillonite and the ethylene-chlorotrifluoroethylene copolymer powder are respectively subjected to micronization treatment using a micronizer and passed through a 100-mesh sieve;

[0044] Step (2), preparation of binder solution:

[0045] The coating solution includes the following raw materials by weight:

[0046]

[0047] Adding a boric acid crosslinker to deionized water and stirring to dissolve to prepare a boric acid aqueous solution; adding polyvinyl alcohol to deionized water and stirring to dissolve at 80 degrees Celsius to prepare a polyvinyl alcohol aqueous solution; then adding the boric acid aqueous solution to the polyvinyl alcohol aqueous solution while stirring, stirring and reacting at 85 degrees Celsius for 35 minutes, then adding micronized montmorillonite and an emulsifier, and high-pressure homogenizing for 90 minutes to obtain a binder solution;

[0048] Step (3) Surface pretreatment of polyester fiber: The polyester fiber is sequentially immersed in a silane coupling agent solution having a mass concentration of 1% (immersion time 23 seconds) and a binder solution (immersion time 65 seconds) (after being taken out of the silane coupling agent solution, it is directly immersed in the binder solution without drying). The polyester fiber is taken out and dried at 80 degrees Celsius to obtain the surface-treated polyester fiber for later use; the silane coupling agent is long-chain octadecyltrimethoxysilane;

[0049] Step (4), electrostatic spraying: 30 g of micronized ethylene-chlorotrifluoroethylene copolymer powder is sprayed onto the surface of the surface-treated polyester fiber by electrostatic spraying; the spraying thickness is 0.2 μm;

[0050] Step (5), baking and cooling: baking the polyester fiber with the ethylene-chlorotrifluoroethylene copolymer powder sprayed on the surface at 200 degrees Celsius, and then cooling to obtain a polyester composite fiber;

[0051] The polyester composite fiber has a fineness of 0.5±0.1 dtex.

[0052] Step 2: Wet papermaking:

[0053] Step 2-1, 6.8 g of polyester composite fiber (fineness 0.5±0.1 dtex), 3.2 g of polypropylene fiber (fineness 1.5±0.2 dtex), 1.5 mL of modified polyether defoamer, and 1.5 mL of 0.025% PEO aqueous solution were added to deionized water and ultrasonically stirred for 60 min until uniformly dispersed to obtain a fiber slurry;

[0054] Step 2-2, the fiber slurry is fed into a wet paper machine to form a non-woven fabric, and excess moisture of the non-woven fabric is removed by roller extrusion at 0.39 MPA and drying at 103° C. to obtain a preliminary non-woven composite fiber layer;

[0055] Step 2-3: The preliminary non-woven composite fiber layer is hot-pressed by a hard pressing roller at 182°C and a soft pressing roller at 75°C in sequence to melt the polypropylene fibers and then heat-bond the fibers into a whole to obtain an acid- and alkali-resistant non-woven fabric for filtration, which is used for filtration in acidic or alkaline environments.

[0056] Example 2

[0057] A method for preparing an acid- and alkali-resistant nonwoven fabric for filtration comprises the following steps:

[0058] Step 1: Preparation of polyester composite fiber:

[0059] Step (1), raw material pretreatment: the montmorillonite and the ethylene-chlorotrifluoroethylene copolymer powder are respectively subjected to micronization treatment using a micronizer and passed through a 100-mesh sieve;

[0060] Step (2), preparation of binder solution:

[0061] The coating solution includes the following raw materials by weight:

[0062]

[0063] Adding a boric acid crosslinker to deionized water and stirring to dissolve to prepare a boric acid aqueous solution; adding polyvinyl alcohol to deionized water and stirring to dissolve at 80 degrees Celsius to prepare a polyvinyl alcohol aqueous solution; then adding the boric acid aqueous solution to the polyvinyl alcohol aqueous solution while stirring, stirring and reacting at 85 degrees Celsius for 35 minutes, and then adding micronized montmorillonite, micronized ethylene-chlorotrifluoroethylene copolymer powder and an emulsifier thereto, and high-pressure homogenizing for 90 minutes to obtain a binder solution;

[0064] Step (3) Surface pretreatment of polyester fiber: The polyester fiber is sequentially immersed in a silane coupling agent solution having a mass concentration of 1% (immersion time 18 seconds) and a binder solution (immersion time 50 seconds) (after being taken out of the silane coupling agent solution, it is directly immersed in the binder solution without drying). The polyester fiber is taken out and dried at 80 degrees Celsius to obtain the surface-treated polyester fiber for later use; the silane coupling agent is a long-chain octadecyltrimethoxysilane;

[0065] Step (4), dip coating: 33 g of micronized ethylene-chlorotrifluoroethylene copolymer powder is sprayed onto the surface of the surface-treated polyester fiber by electrostatic spraying; the spraying thickness is 4 μm;

[0066] Step (5), baking and cooling: baking the polyester fiber with the ethylene-chlorotrifluoroethylene copolymer powder on its surface at 204 degrees Celsius, and then cooling to obtain a polyester composite fiber;

[0067] The polyester composite fiber has a fineness of 0.7±0.1 dtex;

[0068] Step 2: Wet papermaking:

[0069] Step 2-1, 7.3 g of polyester composite fiber (fineness 0.7±0.1 dtex), 2.7 g of polypropylene fiber (fineness 1.5±0.2 dtex), 2.5 mL of modified polyether defoamer, and 2.0 mL of 0.025% PEO aqueous solution were added to deionized water and ultrasonically stirred for 70 min until uniformly dispersed to obtain a fiber slurry;

[0070] Step 2-2: The fiber slurry is fed through a wet paper machine to form a sheet, and excess moisture of the non-woven fabric is removed by roller pressing at 0.41 MPA and drying at 109° C. to obtain a preliminary non-woven composite fiber layer;

[0071] Step 2-3: The preliminary non-woven composite fiber layer is hot-pressed by a hard pressing roller at 187°C and a soft pressing roller at 79°C in sequence to melt the polypropylene fibers and then thermally bond the fibers together to obtain an acid- and alkali-resistant non-woven fabric for filtration, which is used for filtration in acidic or alkaline environments.

[0072] Example 3

[0073] A method for preparing an acid- and alkali-resistant nonwoven fabric for filtration, comprising the following steps:

[0074] Step 1: Preparation of polyester composite fiber:

[0075] Step (1), raw material pretreatment: the montmorillonite and the ethylene-chlorotrifluoroethylene copolymer powder are respectively subjected to micronization treatment using a micronizer and passed through a 100-mesh sieve;

[0076] Step (2), preparation of coating liquid:

[0077] The coating solution includes the following raw materials by weight:

[0078]

[0079] Adding a boric acid crosslinker to deionized water and stirring to dissolve to prepare a boric acid aqueous solution; adding polyvinyl alcohol to deionized water and stirring to dissolve at 80 degrees Celsius to prepare a polyvinyl alcohol aqueous solution; then adding the boric acid aqueous solution to the polyvinyl alcohol aqueous solution while stirring, stirring and reacting at 85 degrees Celsius for 50 minutes, and then adding micronized montmorillonite, micronized ethylene-chlorotrifluoroethylene copolymer powder and an emulsifier thereto, and high-pressure homogenizing for 90 minutes to obtain a coating liquid;

[0080] Step (3) Surface pretreatment of the polyester fiber: The polyester fiber is sequentially immersed in a silane coupling agent solution having a mass concentration of 1% (immersion time 20 seconds) and a binder solution (immersion time 60 seconds) (after being taken out of the silane coupling agent solution, it is directly immersed in the binder solution without drying). The polyester fiber is taken out and dried at 80 degrees Celsius to obtain the surface-treated polyester fiber for later use; the silane coupling agent is a long-chain octadecyltrimethoxysilane;

[0081] Step (4), electrostatic spraying: 35 g of micronized ethylene-chlorotrifluoroethylene copolymer powder is sprayed onto the surface of the surface-treated polyester fiber by electrostatic spraying; the spraying thickness is 5 μm;

[0082] Step (5), baking and cooling: baking the polyester fiber with the ethylene-chlorotrifluoroethylene copolymer powder on its surface at 207 degrees Celsius, and then cooling to obtain a polyester composite fiber;

[0083] The polyester composite fiber has a fineness of 0.8±0.1 dtex;

[0084] Step 2: Wet papermaking:

[0085] Step 2-1, 6.9 g of polyester composite fiber (0.8 ± 0.1 dtex), 3.1 g of polypropylene fiber (fineness 1.5 ± 0.2 dtex), 2.3 mL of modified polyether defoamer, and 1.8 mL of 0.025% PEO aqueous solution were added to deionized water and ultrasonically stirred for 65 min until uniformly dispersed to obtain a fiber slurry;

[0086] Step 2-2, the fiber slurry is fed through a wet paper machine to form a non-woven fabric, and excess moisture is removed from the non-woven fabric by roller pressing at 0.43 MPA and drying at 117° C. to obtain a preliminary non-woven composite fiber layer;

[0087] Step 2-3: The preliminary non-woven composite fiber layer is hot-pressed by a hard pressing roller at 193°C and a soft pressing roller at 82°C in sequence to melt the polypropylene fibers and then heat-bond the fibers into a whole to obtain an acid- and alkali-resistant non-woven fabric for filtration, which is used for filtration in acidic or alkaline environments.

[0088] Comparative Example 1

[0089] A method for preparing an acid- and alkali-resistant nonwoven fabric for filtration, comprising the following steps:

[0090] The same as Example 3, except that no montmorillonite was added to the binder solution.

[0091] Comparative Example 2

[0092] A method for preparing an acid- and alkali-resistant nonwoven fabric for filtration, comprising the following steps:

[0093] The same as Example 3, except that an equal amount of silicon dioxide is added to the binder solution to replace the montmorillonite in Example 3.

[0094] Comparative Example 3

[0095] A method for preparing an acid- and alkali-resistant nonwoven fabric for filtration, comprising the following steps:

[0096] Step 1: Preparation of polyester composite fiber:

[0097] Step (1), raw material pretreatment: ethylene-chlorotrifluoroethylene copolymer powder is micronized using a micronizer and passed through a 100-mesh sieve;

[0098] Step (2), surface pretreatment of polyester fiber: immerse the polyester fiber in a silane coupling agent solution with a mass concentration of 1%, take it out, dry it at 80 degrees Celsius, and set it aside; the silane coupling agent uses long-chain octadecyltrimethoxysilane;

[0099] Step (3), electrostatic spraying: spraying ethylene-chlorotrifluoroethylene copolymer powder onto the surface of the polyurethane fiber using an electrostatic spray gun until the thickness of the ethylene-chlorotrifluoroethylene copolymer reaches 5 μm;

[0100] Step (4), baking and cooling: baking the polyester fiber with the ethylene-chlorotrifluoroethylene copolymer powder on its surface at 207 degrees Celsius, and then cooling to obtain a polyester composite fiber;

[0101] The polyester composite fiber has a fineness of 0.8±0.1 dtex;

[0102] Step 2, wet papermaking: same as Example 3;

[0103] Comparative Example 4

[0104] A method for preparing an acid- and alkali-resistant nonwoven fabric for filtration comprises the following steps:

[0105] Step 1: Preparation of polyester composite fiber:

[0106] Step (1), raw material pretreatment: ethylene-chlorotrifluoroethylene copolymer powder is micronized using a micronizer and passed through a 100-mesh sieve;

[0107] Step (2), preparation of binder solution:

[0108] The coating solution includes the following raw materials by weight:

[0109]

[0110] A water-based epoxy resin emulsion, ethylene-chlorotrifluoroethylene copolymer powder, an emulsifier, and water were mixed and homogenized under high pressure for 80 minutes, and then a curing agent, phthalic anhydride, was added and homogenized under high pressure for 10 minutes to obtain a binder solution;

[0111] Step (2) Surface pretreatment of the polyester fiber: The polyester fiber is sequentially immersed in a silane coupling agent solution having a mass concentration of 1% (immersion time 20 seconds) and a binder solution (immersion time 60 seconds) (after being taken out of the silane coupling agent solution, it is directly immersed in the binder solution without drying). The polyester fiber is taken out and cured at 180 degrees Celsius for 10 minutes to obtain the surface-treated polyester fiber for later use; the silane coupling agent is a long-chain octadecyltrimethoxysilane;

[0112] Step (3), electrostatic spraying: 35 g of micronized ethylene-chlorotrifluoroethylene copolymer powder is sprayed onto the surface of the surface-treated polyester fiber by electrostatic spraying; the spraying thickness is 5 μm;

[0113] Step (4), baking and cooling: baking the polyester fiber with the ethylene-chlorotrifluoroethylene copolymer powder on its surface at 207 degrees Celsius, and then cooling to obtain a polyester composite fiber;

[0114] The polyester composite fiber has a fineness of 0.8±0.1 dtex;

[0115] Since the bending strength of the polyester composite fiber prepared in this embodiment is greatly enhanced, it is no longer suitable for the preparation of non-woven fabrics, and therefore, the subsequent steps are not performed.

[0116] Comparative Example 5

[0117] The preparation method of polyester non-woven fabric for filtration comprises the following steps:

[0118] Step 1: Add 6.9 g of polyester fiber, 2.5 mL of modified polyether defoamer, and 2.0 mL of 0.025% PEO aqueous solution into deionized water, and stir ultrasonically for 70 minutes until uniformly dispersed to obtain a fiber slurry;

[0119] Step 2: The fiber slurry is fed through a wet paper machine to form a nonwoven fabric, and excess moisture is removed from the nonwoven fabric by roller pressing at 0.43 MPA and drying at 105° C. to obtain a preliminary nonwoven composite fiber layer;

[0120] Step 3: The preliminary non-woven composite fiber layer is hot-pressed in sequence using a hard pressing roller at 187°C and a soft pressing roller at 79°C to melt the polypropylene fibers and then thermally bond the fibers together to obtain an acid- and alkali-resistant non-woven fabric for filtration, which is used for filtration in acidic or alkaline environments.

[0121] Comparative Example 6

[0122] The preparation method of polypropylene non-woven fabric for filtration comprises the following steps

[0123] Step 1: 6.9 g of high melting point modified polypropylene fiber, 3.1 g of bonding fiber, 2.5 mL of modified polyether defoamer, and 2.0 mL of 0.025% PEO aqueous solution were added to deionized water and ultrasonically stirred for 70 min until uniformly dispersed to obtain a fiber slurry;

[0124] Step 2: The fiber slurry is fed through a wet paper machine to form a nonwoven fabric, and excess moisture is removed from the nonwoven fabric by roller pressing at 0.43 MPA and drying at 117°C to obtain a preliminary nonwoven composite fiber layer;

[0125] Step 3: The preliminary non-woven composite fiber layer is hot-pressed in sequence using a 130°C hard pressing roller and a 79°C soft pressing roller to melt the polypropylene fibers and then heat-bond the fibers into a whole to obtain an acid- and alkali-resistant non-woven fabric for filtration, which is used for filtration in acidic or alkaline environments.

[0126] Effect Example 1

[0127] The breaking strength and bending stiffness of the polyester composite fibers of Example 3 and Comparative Examples 1-4 were tested. The results are shown in Table 1.

[0128] Table 1

[0129]

[0130] From the data in Table 1, it can be seen that: 1) The bending strength of the polyester composite fibers prepared in Example 3 and Comparative Examples 1-3 is only slightly improved compared to the polyester fiber, and they still meet the requirements of non-woven fabrics and can be used for the preparation of non-woven fabrics; while the bending stiffness of Comparative Example 4 increases significantly and is no longer suitable for the preparation of non-woven fabrics.

[0131] 2) In Comparative Example 1-2, the properties of polyvinyl alcohol changed during the baking and curing process, causing it to become brittle or even decompose, thereby reducing the bonding strength between ethylene-chlorotrifluoroethylene and the polyester resin, causing part of it to fall off from the fiber surface, resulting in a rough appearance.

[0132] 3) In Comparative Example 3, since the ethylene-chlorotrifluoroethylene copolymer and the polyester fiber are connected only by van der Waals force and dipole action, the force between the two is weak, and since the thermal expansion coefficients of the ethylene-chlorotrifluoroethylene copolymer and the polyester fiber are quite different, when directly wrapped, cooling and shrinkage can easily lead to interfacial stress, resulting in a risk of delamination. In severe cases, it may also cause local shedding of the ethylene-chlorotrifluoroethylene copolymer, thereby forming grooves on the fiber surface. In Example 3, due to the introduction of the polyvinyl alcohol intermediate layer, the hydroxyl groups of the polyvinyl alcohol can, on the one hand, undergo an ester exchange reaction with the ester group of the polyester fiber, and on the other hand, can form a coordination bond with the chlorine-containing group of the ethylene-chlorotrifluoroethylene copolymer, thereby improving the bonding strength of the ethylene-chlorotrifluoroethylene copolymer to the outside of the polyester fiber. In addition, when the polyvinyl alcohol is used as the intermediate layer, its flexibility can also relieve the interfacial stress on both sides, avoiding the risk of delamination and local shedding caused by the large difference in thermal expansion coefficient during thermal expansion and contraction, thereby forming a smooth fiber surface.

[0133] Effect Example 2: Mechanical properties and acid and alkali resistance test of non-woven fabrics

[0134] The non-woven fabrics obtained in Example 3 and Comparative Examples 1-3 and 5-6 were used for performance testing. The specific testing method is as follows: the above products were cut into 3 groups of 200mm*15mm non-woven fabric film samples, and the tensile strength of the film samples was measured using a tensile strength tester; the test was conducted three times, and the average value was calculated. The results are shown in Table 2; the tensile strength of the first group of film samples was directly measured; the tensile strength of the second group of film samples was measured after soaking in 5% sodium hydroxide solution for 24 hours; the tensile strength of the third group of film samples was measured after soaking in 5% hydrochloric acid solution for 24 hours.

[0135] Table 2

[0136]

[0137] The higher the tensile strength of the non-woven membrane before soaking, the better its mechanical properties such as wear resistance; the less the tensile strength of the non-woven membrane decreases after soaking, the stronger its acid and alkali resistance; and it can be seen from the data in Table 2: 1) Before soaking, the main fiber is polyester material with higher tensile strength, and the difference between Example 3 and Comparative Examples 1-4, 6 is small; while the tensile strength of Comparative Example 7, in which the main fiber is polypropylene material, is significantly reduced. 2) After alkali or acid immersion, the tensile strength of Example 3 decreased the least; 3) Since no montmorillonite was added to Comparative Example 1, the heat resistance of the polyvinyl alcohol decreased, which led to changes in its performance during production and processing, causing it to become brittle or even decompose, thereby reducing the bonding strength between ethylene-chlorotrifluoroethylene and polyester resin, causing part of it to fall off from the fiber surface, thereby reducing its acid and alkali resistance; 4) Since the silica added to the binder in Comparative Example 2 did not improve the heat resistance of polyvinyl alcohol as much as the montmorillonite in Example 3, as in Comparative Example 1, the performance of polyvinyl alcohol changed during production and processing, causing it to become brittle or even decompose, thereby reducing the bonding strength between ethylene-chlorotrifluoroethylene and polyester resin, causing part of it to fall off from the fiber surface, thereby reducing its acid and alkali resistance; 5) In Comparative Example 3, since the ethylene-chlorotrifluoroethylene copolymer and the polyester fiber are only bonded by van der Waals forces, the bonding strength between the ethylene-chlorotrifluoroethylene copolymer and the polyester fiber is reduced. and dipole effect, the force between the two is weak, and due to the large difference in thermal expansion coefficients between the ethylene-chlorotrifluoroethylene copolymer and the polyester fiber, when directly wrapped, cooling and shrinkage can easily lead to interfacial stress, resulting in a risk of delamination. In severe cases, it may also cause local shedding of the ethylene-chlorotrifluoroethylene copolymer, thereby forming grooves on the fiber surface, affecting the acid and alkali resistance of the non-woven fabric; and in Example 3, due to the introduction of the polyvinyl alcohol intermediate layer, the hydroxyl groups of the polyvinyl alcohol can, on the one hand, undergo an ester exchange reaction with the ester group of the polyester fiber, and on the other hand, can form a coordination bond with the chlorine-containing group of the ethylene-chlorotrifluoroethylene copolymer, thereby improving the bonding strength of the ethylene-chlorotrifluoroethylene copolymer on the outside of the polyester fiber. In addition, when polyvinyl alcohol is used as the intermediate layer, its flexibility can also relieve the interfacial stress on both sides, avoiding the risk of delamination and local shedding due to the large difference in thermal expansion coefficients during thermal expansion and contraction.

[0138] Effect example 3: Hydrophobic effect

[0139] The nonwoven fabrics obtained in Example 3 and Comparative Examples 1-3 and 5-6 were subjected to performance tests. The specific testing method is as follows: the above products were cut into 1 cm × 5 cm nonwoven film-like glass plates, and three points on the nonwoven fabric were tested with deionized water, and the average value was taken; the results are shown in Table 3; among them, the larger the contact angle, the better the hydrophobic performance of the nonwoven fabric.

[0140] Table 3

[0141] Contact angle°1 Contact angle °2 Contact angle °3 average value Example 3 91.56 89.46 92.11 91.04 Comparative Example 1 79.68 75.62 76.85 77.38 Comparative Example 2 83.35 86.87 87.51 85.91 Comparative Example 3 89.56 87.94 92.36 89.95 Comparative Example 5 79.65 74.37 76.95 76.99 Comparative Example 6 80.36 83.68 85.52 83.19

[0142] The above-described embodiments are only preferred embodiments of the present invention and are not exhaustive of all feasible implementations of the present invention. For those skilled in the art, any obvious modifications made thereto without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. An acid and alkali resistant nonwoven fabric for filtration, characterized in that: It is made of polypropylene fiber and polyester composite fiber through a wet papermaking process; the polyester composite fiber is a core-sheath structure, the core layer is polyester fiber, the sheath layer is ethylene-chlorotrifluoroethylene copolymer, and an adhesive layer is provided between the core layer and the sheath layer.

2. The acid- and alkali-resistant nonwoven fabric for filtration according to claim 1, characterized in that: The mass ratio of the polypropylene fiber to the polyester composite fiber is 2.7-3.3:6.5-7.

3.

3. The acid- and alkali-resistant nonwoven fabric for filtration according to claim 1, wherein: The preparation method of the polyester composite fiber comprises the following steps: Step (1), preparation of a binder: adding a boric acid crosslinker to deionized water, stirring and dissolving to prepare a boric acid aqueous solution; adding polyvinyl alcohol to deionized water, stirring and dissolving at 80 degrees Celsius to prepare a polyvinyl alcohol aqueous solution; then adding the boric acid aqueous solution to the polyvinyl alcohol aqueous solution while stirring, stirring and reacting at 80-100 degrees Celsius for 35 minutes, then adding montmorillonite and an emulsifier thereto, and high-pressure homogenizing for 90 minutes to obtain a binder solution; Step (2) Surface pretreatment of the polyester fiber: immersing the polyester fiber in a silane coupling agent solution and a binder solution in sequence, taking it out, and drying it at 80 degrees Celsius to obtain the preliminarily treated polyester fiber for later use; Step (3), electrostatic spraying: using electrostatic spraying technology to spray ethylene-chlorotrifluoroethylene powder onto the surface of the polyester fiber coated with the surface pretreatment; Step (4), baking and cooling and drying: baking the polyester fiber with ethylene-chlorotrifluoroethylene sprayed on the surface, cooling to obtain the ethylene-chlorotrifluoroethylene coating layer, and then adjusting the fiber length to obtain the polyester composite fiber.

4. The acid- and alkali-resistant nonwoven fabric for filtration according to claim 3, wherein: In step (1), the mass percentage of each raw material of the binder is:

5. The acid- and alkali-resistant nonwoven fabric for filtration according to claim 3, characterized in that: In step (2), the silane coupling agent is octadecyltrimethoxysilane, The mass concentration of the silane coupling agent solution is 0.5-1.5%.

6. The acid- and alkali-resistant nonwoven fabric for filtration according to claim 3, characterized in that: In step (2), the polyester fiber is immersed in the silane coupling agent solution for 15-25 seconds, and in the binder solution for 50-70 seconds.

7. The acid- and alkali-resistant nonwoven fabric for filtration according to claim 3, characterized in that: In step (3), the ethylene-chlorotrifluoroethylene copolymer powder is further crushed by a micro-powder grinder before spraying, and sieved by a 100-mesh screen; the spraying thickness of the ethylene-chlorotrifluoroethylene is 2-5 microns; In step (4), the baking treatment temperature is 200 degrees Celsius and the time is 30-60 minutes; the fineness of the polyester composite fiber is 0.5-0.8 dtex.

8. A method for preparing an acid- and alkali-resistant nonwoven fabric for filtration, characterized in that: The steps include: Step 1: Add polyester composite fiber, polypropylene fiber, defoaming agent, and PEO aqueous solution into deionized water, and stir ultrasonically for 60 minutes until uniformly dispersed to obtain fiber slurry; Step 2: The fiber slurry is fed through a wet paper machine to form the nonwoven fabric, and excess moisture is removed from the nonwoven fabric by roller pressing and drying at 103°C to obtain a preliminary nonwoven composite fiber layer; Step 3: The preliminary non-woven composite fiber layer is hot-pressed by a hard pressing roller and a soft pressing roller in sequence, so that the polypropylene fibers are melted and then the fibers are thermally bonded into a whole to obtain an acid and alkali resistant non-woven fabric.

9. The method for preparing an acid- and alkali-resistant nonwoven fabric for filtration according to claim 8, characterized in that: In step 1, the fineness of the polypropylene fiber is 1.2-1.7 dtex; and the concentration of the PEO aqueous solution is 0.02-0.03%.

10. The method for preparing an acid- and alkali-resistant nonwoven fabric for filtration according to claim 8, characterized in that: In step 3, the temperature of the hard pressing roller is 182°C, and the temperature of the soft pressing roller is 75°C. The defoamer is a modified polyether defoamer.

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