A glass fiber filter material with persistent and broad pH-range positive charge, its preparation method and application

Abstract

The present invention discloses a glass fiber filter material with persistent and broad pH range of positive charge, its preparation method and application. The glass fiber filter material with persistent and broad pH range of positive charge is obtained by surface modification of a glass fiber filter substrate with an aqueous cationic epoxy resin system and a curing agent reactive with glass fiber. Moreover, the fibers of the prepared filter material can maintain a stable positive charge property within a relatively broad pH range (pH = 3 - 11) and have a long service time in water filtration. In addition, the prepared glass fiber filter material has excellent strength performance and water resistance, and can be applied to the efficient filtration of sub-micron, nano and smaller size pollutants in water filtration.

Description

Technical Field

[0001] The present invention relates to the technical field of filtration and separation, and particularly relates to a glass fiber filter material with a persistent and broad pH range of positive charge, a preparation method thereof, and an application thereof. Background Art

[0002] The rapid development of industry has led to environmental hazards and various human diseases caused by water pollution and water quality problems, which have attracted much attention. There are various particulate pollutants in water. For small-sized particulate pollutants, filtration through filter materials is an effective removal method. As is well known, filtration is to remove pollutants from a fluid (liquid or gas) using a porous medium to make the fluid reach the required cleanliness level. The filtration accuracy is the ability of the filter medium to block solid particles during use. Generally, the filtration accuracy is improved by adjusting the pore size of the filter material. However, the smaller the pore size, the greater the resistance of the filter material and the shorter the service life. Therefore, for sub-micron-sized pollutants in water, traditional filter materials that filter by interception cannot solve the contradiction between filtration accuracy and filtration resistance, and thus cannot meet the actual application requirements, which is the key problem existing currently.

[0003] Since fine solid particles, bacteria, viruses, etc. in water usually have a negatively charged surface, when a solution containing these negatively charged impurities passes through a positively charged filter medium, due to electrostatic action, these sub-micron-sized or smaller-sized impurities will be adsorbed by the membrane to achieve the purification purpose. Therefore, if a persistent and stable positive charge property can be constructed on the surface of the filter material, the filter material can further capture small-sized particulate pollutants through electrostatic adsorption in addition to the physical sieving effect of the pore size. In addition, this adsorption behavior caused by introducing charged groups has a high selectivity for charged particles, and at the same time, the hydrophilicity of the material surface is enhanced and the water flux is increased, which is expected to solve the contradictory relationship between the filtration efficiency and resistance of the filter material.

[0004] The glass fiber filter material is a filter material prepared by wet papermaking molding with glass fiber and glass wool as raw materials. Compared with other filter materials, it has excellent filtration performance, uniform pore distribution, and high dirt-holding capacity. There are mainly two methods for constructing a positively charged surface on the filter material. One is to prepare the filter material with fiber materials that inherently carry positive charges. However, there are few types of such fibers, and the selection is limited. The other is to perform surface modification or coating on the existing filter material to make its surface carry positive charges. The most common method is to quaternize the surface of the filter material. The literature [Xia Xue, Li Guoping, Luo Jiyue, Ma Yiwen. Improving the Zeta potential of the glass fiber membrane surface by quaternary ammonium salt grafting, Water Purification Technology, 2020, 39(03): 82-88] uses a glass fiber membrane as the matrix, through plasma treatment, and then chemically grafts organosilicon quaternary ammonium salt with Si-QAS antibacterial agent and tetraethyl orthosilicate reagent to prepare a positively charged glass fiber membrane, and the Zeta potential value can reach 27.35 mV. However, due to the poor fiber binding force between the glass fiber filter materials, the structure of the glass fiber base paper is loose. In fact, usually, it is necessary to enhance the glass fiber filter material with a reinforcing resin to meet the actual application requirements. Chinese Patent CN113737570A reports that a glass fiber filter material with a positive Zeta potential is obtained by coating the glass fiber filter material with a cationic resin as a reinforcing resin, and the filtration efficiency for 1μm particles reaches 99.3%. However, the above reports do not study the filtration efficiency for particles below 1 micron, nor do they describe the specific preparation method and route of the cationic resin. Chinese Patent 202180060496.X prepares a positively charged filter material with excellent removal performance for charged particles by means of plasma surface treatment and coating a positive charge coating, which has excellent flow rate and filtration pressure. However, the positive charge on the surface of the filter material of this invention is under the condition of pH = 7, and the positively charged property in a wider pH range is not considered.

[0005] If the positive charge on the surface of the filter material cannot exist stably and persistently, then the electrostatic attraction between the filter material fibers and the particulate contaminants will disappear. In addition, due to certain impurities in the environment or other reasons, the pH of the water body may change, and the positive charge on the surface of the filter material has a great relationship with the pH. If the filter material cannot exhibit positive charge in a relatively wide pH range, when the surface of the filter material becomes negatively charged due to the environmental pH, then there will not only be no attraction between the filter material and the contaminants, but instead a repulsive force will be presented, thus reducing the filtration efficiency of the filter material. Therefore, preparing a glass fiber filter material that can maintain a stable positive charge property in a wide pH range has important and broad application prospects. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the problem that existing filter media cannot solve the problem between filtration efficiency and filtration resistance for filtering sub-micron-sized particulate matters in water, and a preparation method and application of a glass fiber filter media with persistence and a positively charged surface in a wide pH range are proposed. The glass fiber filter media with persistence and a positively charged surface in a wide pH range is prepared by using a cationic epoxy resin and a curing agent reactive with glass fiber as a reinforcing resin system.

[0007] On the one hand, in the present invention, hydrophilic quaternary ammonium salts are introduced into the main chain structure of a cationic epoxy resin containing multiple (4 - 8) epoxy groups, which can simultaneously achieve the hydrophilicity and cationic modification of the resin; at the same time, sufficient epoxy groups can be retained to participate in the curing reaction with the curing agent, so that the cured resin has excellent water resistance and can meet the application requirements in the field of water filtration materials. On the other hand, the curing agent used is a silane coupling agent - polyethyleneimine addition product reactive with glass fiber. Polyethyleneimine itself has a high positive charge density in the molecular structure, and the silanol groups in the silane coupling agent - polyethyleneimine addition product can form chemical bonds with the hydroxyl groups on the surface of the glass fiber and then graft onto the filter media, further enhancing the interfacial bonding between the glass fiber and the reinforcing resin, which is beneficial to further improving the water resistance of the reinforced filter media.

[0008] The surface of the reinforced glass fiber filter media endows the filter media with excellent strength performance and water resistance, and at the same time endows the glass fiber with persistence and positively charged properties in a wide pH range. The treated filter media can filter particulate pollutants in water through both interception and electrostatic adsorption, achieving high filtration efficiency under the action of low resistance.

[0009] In order to achieve the above-mentioned invention purpose, the present invention adopts the following technical scheme:

[0010] The present invention provides a glass fiber filter media with persistent and positively charged properties in a wide pH range. More specifically, it is a water-based cationic epoxy resin / amine curing agent composite emulsion surface-coated and constructed positively charged glass fiber filter material, which is prepared by a method including the following steps:

[0011] Ⅰ. In a reaction kettle equipped with a stirring device, a condensing device, and a temperature control device, an epoxy resin with a molecular structure containing 4 - 8 epoxy groups and a secondary amine modifier are mixed in a certain proportion, and a diluent accounting for 20 - 40% of the mass of the epoxy resin is added, and the mixture is heated to 65 - 80 °C and stirred for 2 - 6 h;

[0012] Ⅱ. After cooling to 50 - 60 °C, an acid equimolar to the secondary amine modifier is added for neutralization to obtain a water-based cationic epoxy resin emulsion;

[0013] Ⅲ. Dilute by adding 3 - 5 times the mass of water of the epoxy resin under high - speed stirring at 300 - 800 rpm;

[0014] Ⅳ. Carry out vacuum distillation to remove most of the solvents, and then the aqueous cationic epoxy resin can be obtained;

[0015] Ⅴ. In a reaction kettle equipped with a stirring device, a condensing device, and a temperature - controlling device, add a silane coupling agent containing epoxy groups and polyethyleneimine PEI with a branched structure to 4 - 15 times of water, heat up to 70 - 90 °C and react for 2 - 4 h, then an amine - type curing agent with reactive activity can be prepared;

[0016] Ⅵ. Mix the prepared aqueous cationic epoxy resin and the prepared amine - type curing agent in a certain proportion, and then dilute to a suitable concentration to obtain an aqueous cationic enhanced resin system;

[0017] Ⅶ. Apply the prepared aqueous cationic enhanced resin system to the glass fiber substrate by means of impregnation, spraying, or curtain coating, etc., and finally dry and cure;

[0018] After completing the above operations, a glass fiber filter material with a positive charge in a persistent and broad pH range can be obtained.

[0019] Preferably, the epoxy resin containing 4 - 8 epoxy groups in the molecular structure is selected from o - cresol novolac epoxy resin or bisphenol A novolac epoxy resin, and the structural formulas are shown as Formula (1) and Formula (2) respectively:

[0020]

[0021]

[0022] Preferably, the secondary - amine modifier is selected from one or more mixtures of diethanolamine, methylethanolamine, diethylamine, and diisopropylamine, and the dosage of the secondary - amine modifier accounts for 30 - 60% (defined as the ring - opening rate) of the molar number of epoxy groups in the epoxy resin.

[0023] More preferably, the secondary - amine modifier is diethanolamine and methylethanolamine, and the dosage of the secondary - amine modifier accounts for 35 - 50% of the molar number of epoxy groups in the epoxy resin.

[0024] Preferably, the silane coupling agent containing epoxy groups is selected from one of 3 - glycidoxypropyltrimethoxysilane (A - 187), 3 - glycidoxypropyltriethoxysilane (A - 1871), β - (3,4 - epoxycyclohexyl)ethyltrimethoxysilane (A - 186), and β - (3,4 - epoxycyclohexyl)ethyltriethoxysilane (A - 1861).

[0025] Preferably, the molecular weight of the branched polyethyleneimine is 3000 - 15000.

[0026] More preferably, the molecular weight of the branched polyethyleneimine is 5000 - 10000.

[0027] Preferably, the molar ratio of the branched polyethyleneimine to the silane coupling agent containing epoxy groups is 1.0:10.0 - 20.0.

[0028] More preferably, the molar ratio of the branched polyethyleneimine to the silane coupling agent containing epoxy groups is 1.0:15.0 - 20.0.

[0029] Preferably, the ratio of the aqueous cationic epoxy resin to the amine curing agent is such that the molar ratio of the epoxy groups in the aqueous cationic epoxy resin to the secondary amino groups in the curing agent is 1.0:1.0 - 1.3.

[0030] More preferably, the ratio of the aqueous cationic epoxy resin to the amine curing agent is such that the molar ratio of the epoxy groups in the aqueous cationic epoxy resin to the secondary amino groups in the curing agent is 1.0:1.1 - 1.2.

[0031] Preferably, the diluent is ethanol, tert-butanol or methyl ethyl ketone.

[0032] Preferably, the acid includes organic acid or inorganic acid. More preferably, the acid is acetic acid.

[0033] Preferably, the sizing amount of the aqueous cationic modified reinforcing resin system accounts for 5 - 10 wt% of the mass of the glass fiber substrate, and the average pore diameter of the glass fiber substrate is 1.5 - 3.5 μm.

[0034] More preferably, the sizing amount of the aqueous cationic modified reinforcing resin system accounts for 5 - 8 wt% of the mass of the glass fiber substrate, and the average pore diameter of the glass fiber substrate is 2.0 - 3.0 μm.

[0035] The positively charged glass fiber filter material with a persistent and broad pH range prepared above, the "persistent" means it can be used for a long time (more than 60 days) in water filtration; the "broad pH range" means it can still maintain a stable positively charged property within a relatively broad range (pH = 3 - 11). In addition, the prepared glass fiber filter material has excellent strength performance and water resistance.

[0036] Compared with the prior art, the beneficial effects of the present invention are:

[0037] The aqueous cationic epoxy resin / amine curing agent composite emulsion of the present invention is an environmentally friendly cationic enhanced resin system. Both the epoxy resin and the curing agent have a high positive charge property. The positively charged fiberglass filter material obtained after being treated with the enhanced resin has excellent strength performance and water resistance, and can be used for a long time in water filtration and maintain a stable positive charge property. In addition, the fiberglass filter material treated with the enhanced resin can still maintain a stable positive charge property within a relatively wide range. The positively charged fiberglass filter material prepared by the present invention can achieve high-efficiency filtration of particulate pollutants with a size of sub-micron and below in water under a low resistance, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The present invention will be described in detail below with reference to the accompanying drawings.

[0039] Figure 1 It is a schematic process flow diagram for the preparation of the aqueous cationic epoxy resin / amine curing agent composite emulsion described in the present invention.

[0040] Figure 2 It is an SEM image of the positively charged fiberglass filter material prepared in Example 9 after water filtration test.

[0041] Figure 3 It is an SEM image of the positively charged fiberglass filter material prepared in Comparative Example 9 after water filtration test.

[0042] Figure 4 It is a structural design diagram of the experimental bench for the water filtration performance of the filter material of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] The following further describes a positively charged fiberglass filter material with a persistent and broad pH range, its preparation method and application with reference to specific embodiments. Those skilled in the art can understand that these embodiments are only used to illustrate the present invention, but the protection scope of the present invention is not limited thereto.

[0044] The experimental methods in the following embodiments are all conventional methods unless otherwise specified. The raw materials, reagent materials, etc. used in the following embodiments are all commercially available products unless otherwise specified.

[0045] Please refer to Figure 1 , which details the main steps of the preparation process flows of the aqueous cationic epoxy resin, amine curing agent, and positively charged fiberglass filter material in the examples and comparative examples.

[0046] The fiberglass base paper used in the following examples was prepared by the following method.

[0047] Preparation of fiberglass base paper 1: Mix 475-79 glass wool and 6 mm chopped fiberglass in a ratio of 8:2, and use a defibrator to defibrate. The defibrating speed is 10,000 revolutions, control pH = 2.5-3.5, and the basis weight is 38 g / m 2 , after uniform defibration, pour the pulp into a former, dehydrate and form, and then dry at 105 °C to obtain the fiberglass filter base paper. The average pore size of the fiberglass base paper is measured to be 2.13 μm.

[0048] Preparation of fiberglass base paper 2: Use a defibrator to defibrate 475-79 glass wool. The defibrating speed is 10,000 revolutions, control pH = 2.5-3.5, and the basis weight is 38 g / m 2 , after uniform defibration, pour the pulp into a former, dehydrate and form, and then dry at 105 °C to obtain the fiberglass filter base paper. The average pore size of the fiberglass base paper is measured to be 1.05 μm.

[0049] Preparation of fiberglass base paper 3: Mix 475-79 glass wool and 6 mm chopped fiberglass in a ratio of 6:4, and use a defibrator to defibrate. The defibrating speed is 10,000 revolutions, control pH = 2.5-3.5, and the basis weight is 38 g / m 2 , after uniform defibration, pour the pulp into a former, dehydrate and form, and then dry at 105 °C to obtain the fiberglass filter base paper. The average pore size of the fiberglass base paper is measured to be 5.20 μm.

[0050] Examples 1-4 and Comparative Examples 1-2

[0051] Examples 1-4 and Comparative Examples 1-2 prepared a waterborne cationic epoxy resin. The raw material composition is shown in Table 1 and is prepared by a method including the following steps:

[0052] Ⅰ. In a reaction kettle equipped with a stirring device, a condensing device, and a temperature control device, mix an epoxy resin with a molecular structure containing 4-8 epoxy groups and a secondary amine modifier in a certain ratio, then add tert-butanol accounting for 30% of the mass of the epoxy resin, and heat to 65-80 °C and stir and react for 2-6 h.

[0053] Ⅱ. After cooling to 50-60 °C, add acetic acid equimolar to the secondary amine modifier for neutralization to obtain a waterborne cationic epoxy resin emulsion.

[0054] Ⅲ. Add 3-5 times the mass of water of the epoxy resin for dilution at a stirring speed of 300-800 rpm.

[0055] Ⅳ. Carry out vacuum distillation to remove most of the solvents. Then the described waterborne cationic epoxy resin can be obtained.

[0056] Table 1 Raw material composition of waterborne cationic epoxy resin in Examples 1-4 and Comparative Examples 1-2

[0057]

[0058] Examples 5 to 8 and Comparative Examples 3 to 4

[0059] Examples 5 to 8 and Comparative Examples 3 to 4 prepared an amine curing agent. The raw material composition is shown in Table 3 and was prepared by a method including the following steps:

[0060] In a reaction kettle equipped with a stirring device, a condensing device, and a temperature control device, the silane coupling agent KH-560 and branched-chain PEI were added to water, and the temperature was raised to 70 - 90 °C and reacted for 2 - 4 h to prepare a reactive amine curing agent.

[0061] Table 2 Raw material composition of the amine curing agents in Examples 5 to 8 and Comparative Examples 3 to 4

[0062]

[0063] Examples 9 to 12 and Comparative Examples 5 to 10

[0064] Preparation of positively charged glass fiber filter paper in Examples 9 to 12: After the waterborne epoxy resin prepared in Examples 1 to 4 was compounded with the curing agent prepared in Examples 5 to 8, the molar ratio of the epoxy groups in the waterborne cationic epoxy resin to the molar ratio of the secondary amino groups in the reactive amine curing agent was 1.0:1.0. (The epoxy resin prepared in Example 1 and the curing agent prepared in Example 5 were compounded and applied to the reinforcement of glass fiber base paper 1 to obtain Example 9, the epoxy resin prepared in Example 2 and the curing agent prepared in Example 6 were compounded and applied to the reinforcement of glass fiber base paper 1 to obtain Example 10, the epoxy resin prepared in Example 3 and the curing agent prepared in Example 7 were compounded and applied to the reinforcement of glass fiber base paper 1 to obtain Example 11, and the epoxy resin prepared in Example 4 and the curing agent prepared in Example 8 were compounded and applied to the reinforcement of glass fiber base paper 1 to obtain Example 12). The resin sizing amount in Examples 9 to 12 was controlled within the range of 6.0 ± 0.5%.

[0065] Comparative Examples 5 to 6: The epoxy resin prepared in Example 1 and the curing agent prepared in Example 5 were compounded and applied to the reinforcement of glass fiber base paper 2 to obtain Comparative Example 5, and the epoxy resin prepared in Example 1 and the curing agent prepared in Example 5 were compounded and applied to the reinforcement of glass fiber base paper 3 to obtain Comparative Example 6. The resin sizing amount in Comparative Examples 5 to 6 was controlled within the range of 6.0 ± 0.5%.

[0066] Comparative Examples 7 - 8: The waterborne epoxy resin prepared in Comparative Example 1 was compounded with the curing agent prepared in Comparative Example 3 and then applied to the reinforcement of fiberglass filter paper 1 to obtain Comparative Example 7; the waterborne epoxy resin prepared in Comparative Example 2 was compounded with the curing agent prepared in Comparative Example 4 and then applied to the reinforcement of fiberglass filter paper 1 to obtain Comparative Example 8. In Comparative Examples 7 - 8, the resin sizing amount was controlled within the range of 6 ± 0.5%.

[0067] Comparative Example 9: A commercially available waterborne cationic strengthening agent (Kymene TM 777LX, Solenis Company) was selected; the above - mentioned commercially available cationic resin impregnating solution was used to impregnate the fiberglass base paper to obtain Comparative Example 9. In Comparative Example 9, the resin sizing amount was controlled within the range of 6 ± 0.5%.

[0068] Comparative Example 10: The filter material after being strengthened with a common anionic acrylic resin on the market (Dow, USA, PRIMAL AS - 8508) was used as Comparative Example 10. In Comparative Example 10, the resin sizing amount was controlled within the range of 6 ± 0.5%.

[0069] The tensile strength test was carried out in accordance with GB / T12914 - 2018. A tensile strength tester (model: CE062, L&W Company, Sweden) was used to test the tensile strength and elongation at break of the fiberglass filter paper. The length of the specimen was 100 mm and the width was 15 mm.

[0070] Tensile strength after water resistance test: The positively charged fiberglass filter material was immersed in deionized water at 50 °C for 72 h, and then the tensile strength of the fiberglass filter material was measured again.

[0071] Zeta potential test of fiberglass filter material: The Zeta potential meter using the streaming potential method (model: SZP - 06, Mütek Company, Germany) was used for the test. The fiberglass filter material was disintegrated into a slurry and configured into a 500 - ml solution, and the slurry concentration was controlled to be less than 4%. The surface charge of the fiberglass slurry was tested.

[0072] Zeta potential test after water resistance test: The positively charged fiberglass filter material was immersed in deionized water at 50 °C for 72 h, and then the potential of the fiberglass filter material was measured again.

[0073] Test of filtration performance (filtration efficiency and resistance): Referring to the European standard EN 13443 - 2 《Water conditioning equipment inside buildings - mechanical filters》, a test bench for the water filtration performance of the filter material was designed using the single - pass method and the corresponding test methods were specified. The water filtration performance test bench is as Figure 4As shown in the figure, where: 1 - test tank; 2 - high-speed stirrer; 3 - thermometer; 4 - stop valve; 5 - coarse filter; 6 - hydraulic pump; 7 - throttle valve; 8 - sampling valve; 9 - flowmeter; 10 - pressure gauge; 11 - differential pressure sensor; 12 - filter media clamp; 13 - liquid collection tank. The experimental conditions for the water filtration efficiency test are as follows: water flow rate is 75 L / h, pollutant flow rate is 0.75 ml / h, test time is 60 min, and test area is 78.5 cm 2 , the test medium is deionized water, and the pollutant is a polystyrene latex ball suspension. The polystyrene latex ball suspension diluted to a particle concentration of 2000 - 20000 particles / ml is passed through the filter paper at a surface flow rate of 5 - 10 cm / min, and the number of experimental particles in the upstream and downstream of the filter paper sample is measured, and the water filtration efficiency of the filter paper is calculated. Samples are taken at the upstream sampling port every 10 minutes and at the downstream sampling port every 5 minutes, and the filtration efficiency of the filter media is obtained by calculating the number of particles upstream and downstream. At the same time, the differential pressure gauge reading is recorded every 5 minutes, and this data represents the filtration resistance.

[0074] Test Example 1

[0075] Performance test of the positively charged fiberglass filter media obtained in Examples 9 - 12 and the fiberglass filter media obtained in Comparative Examples 5 - 10.

[0076] Measure the positively charged fiberglass filter media obtained in Examples 9 - 12 and the fiberglass filter media obtained in Comparative Examples 5 - 10, and measure the Zeta potential, strength performance, filtration performance, etc. under the condition of pH = 7. The test results are shown in Table 3.

[0077] Table 3 Performance test results of each example and comparative example (pH = 7)

[0078]

[0079]

[0080] It can be seen from the test results in Table 3 that the filter media obtained in Examples 9 - 12 all have a relatively high Zeta potential, and the Zeta potential can still be well retained after soaking in water, indicating its water resistance and persistence; in addition, the strength of the filter media after being treated with cation resin is greatly improved, and the strength performance can also be well retained after soaking in water, further indicating that the resin system has excellent water resistance; and the filtration efficiency of the filter media for 300 nm particle pollutants can be maintained above 94%, and the resistance is lower than 8 Kpa, indicating that the obtained filter media has the function of high efficiency and low resistance.

[0081] The Zeta potential, tensile strength of Comparative Examples 5 and 6, and the Zeta potential and strength after immersion in water are not much different from those of the Examples, which also proves that the enhanced resin system obtained by compounding the epoxy resin prepared in Example 1 and the curing agent prepared in Example 5 has excellent effects. However, in Comparative Example 5, since the pore diameter of the glass fiber material used is only 1.05 μm, although the decrease in pore diameter can increase its filtration efficiency to 97.7%, its resistance increases exponentially, which will lead to a significant decrease in its service life. In Comparative Example 6, since the pore diameter of the glass fiber material used is 5.2 μm, although the increase in pore diameter can reduce the filtration resistance, its filtration efficiency decreases significantly, only reaching 81.7%. In Comparative Example 7, due to the low ring-opening rate of the cationic epoxy resin used, the cation density of its molecular structure formula decreases, resulting in a decrease in the Zeta potential on the surface of the filter medium, and the electrostatic adsorption effect of the filter medium on particulate pollutants decreases significantly, so the filtration efficiency also decreases significantly. In Comparative Example 8, due to the too high ring-opening rate of the waterborne epoxy resin, too few groups of the epoxy resin participating in the curing reaction in the resin system, the crosslinking density of the cured resin decreases, resulting in a decrease in the water resistance of the resin system. Therefore, its Zeta potential decreases significantly after soaking in water, and its strength performance also decreases significantly. In Comparative Example 9, a commercial waterborne cationic enhancer is used for enhancement. After enhancement, the Zeta potential of the filter medium is low, the filtration efficiency is low, and the water resistance strength performance is poor. In Comparative Example 10, a commercial anionic acrylic resin is used as the enhancer, and its Zeta potential is negative and the filtration efficiency is very low.

[0082] Test Example 2

[0083] Zeta potential tests of the positively charged glass fiber filter media obtained in Examples 9 to 11 and the glass fiber filter media obtained in Comparative Examples 7 and 9 under different pH conditions. The results are shown in Table 4.

[0084] Table 4 Zeta potential test results of each Example and Comparative Example under different pH conditions

[0085]

[0086] As can be seen from Table 4, for the filter media prepared in the present invention, within the range of pH = 3 to 11, the surface of the filter media can maintain a positively charged state, while for Comparative Example 7 and Comparative Example 9, it is difficult to maintain a positively charged state after pH exceeds 9. This can be inferred from the difference in the ζ potential test results that the cation group density of the cation resin and curing agent system in the Examples is much higher than that in the Comparative Examples. Even under alkaline conditions (OH - ion concentration is relatively high), the surface cationic properties can still be maintained.

[0087] Figure 2 SEM picture of the positively charged glass fiber filter medium prepared in Example 9 after water filtration testFigure 3 SEM image of the positively charged glass fiber filter media prepared in Comparative Example 9 after water filtration test. It can be seen from the comparison that due to the strong positive charge property on the surface of the filter media fibers prepared in Example 9, obvious electrostatic adsorption can occur between the fibers and pollutants. As a result, the filter media fibers can effectively capture pollutants of nanoscale size, and it can be observed that the filter media is covered with particulate pollutants intercepted by filtration. For the commercially available cationic resin used in Comparative Example 9, the positive charge density is much lower than that of the resin used in Example 9. Therefore, the surface positive charge density of the treated filter media is significantly reduced, and the electrostatic adsorption with pollutants is significantly less, resulting in a significant decrease in the adsorption and capture force on pollutants and a significant decrease in filtration efficiency. Therefore, the number of pollutants on the filtered filter media decreases significantly.

[0088] Test Example 3

[0089] The ζ potential changes of the glass fiber filter media of Example 9 and Comparative Example 9 were tested after soaking in water for different times. The results are shown in Table 5.

[0090] Table 5 ζ potential of the glass fiber filter media of Example 9 and Comparative Example 9 after soaking in water for different times

[0091]

[0092] It can be seen from Table 5 that after the filter media prepared in the present invention is soaked in water for 60 days, its filtration performance and ζ potential change little. For the filter media prepared in the comparative example, its filtration performance has decreased significantly, further indicating that the filter media prepared in the present invention has lasting stability in filtration performance.

[0093] The above embodiments are only the preferred embodiments of the present invention, which are only used to explain the present invention, rather than limiting the present invention. Any changes, substitutions, modifications, etc. made by those skilled in the art without departing from the spirit and essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for preparing a filter material having a long-lasting positive charge over a wide pH range, characterized in that: The preparation process is as follows: (1) Preparation of water-based cationic epoxy resin system: After mixing an epoxy resin having 4-8 epoxy groups in its molecular structure with a secondary amine modifier, a diluent is added, and the mixture is heated to 65-80° C. for reaction for 2-6 hours. After cooling to 50-60° C., an acid in an amount equimolar to that of the secondary amine modifier is added for neutralization. Water in an amount 3-5 times the mass of the epoxy resin is added under stirring to prepare a water-based cationic epoxy resin. The amount of the secondary amine modifier used accounts for 30-60% of the molar number of epoxy groups in the epoxy resin. (2) Preparation of a curing agent reactive with glass fiber: Add an epoxy-containing silane coupling agent and a branched polyethyleneimine to 4-15 times the volume of water, heat to 70-90° C. and react for 2-4 hours to prepare a reactive amine curing agent; (3) compounding the waterborne cationic epoxy resin prepared in step (1) and the curing agent prepared in step (2), and diluting them to a suitable concentration to obtain a waterborne cationic enhanced resin system; (4) applying sizing to a glass fiber substrate by dipping, spraying or curtain coating the prepared aqueous cationic enhanced resin system, controlling the amount of sizing to account for 5-10 wt% of the base paper mass, and the average pore size of the glass fiber substrate is 1.5-3.5 μm. After drying and curing, a glass fiber filter material having a long-lasting positive charge in a wide pH range can be obtained. The glass fiber filter material can be used in water filtration for more than 60 days and maintains a stable positive charge property in the range of pH = 3-11.

2. The method for preparing a filter material having a long-lasting positive charge over a wide pH range according to claim 1, characterized in that: The epoxy resin containing 4-8 epoxy groups in the molecular structure is selected from o-cresol epoxy resin or bisphenol A novolac epoxy resin, and the structural formulas are shown in formula (1) and formula (2) respectively:

3. The method for preparing a filter material having a persistent and wide pH range of positive charge according to claim 1, characterized in that: The secondary amine modifier is selected from a mixture of diethanolamine, methylethanolamine, diethylamine and diisopropylamine; the diluent is ethanol, tert-butyl alcohol or butanone, and the amount used is 20-40% of the mass of the epoxy resin; and the acid includes an organic acid or an inorganic acid.

4. The method for preparing a filter material having a long-lasting positive charge over a wide pH range according to claim 1, characterized in that: The epoxy-containing silane coupling agent is selected from 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropyltriethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane and β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

5. The method for preparing a filter material having a long-lasting positive charge over a wide pH range according to claim 1, characterized in that: The molecular weight of the branched polyethyleneimine is 3000-15000.

6. The method for preparing a filter material having a persistent and wide pH range positive charge according to claim 1, characterized in that: The molar ratio of the branched polyethyleneimine to the epoxy-containing silane coupling agent is 1.0:10.0-20.

0.

7. The method for preparing a filter material having a long-lasting positive charge over a wide pH range according to claim 1, characterized in that: The ratio of the water-based cationic epoxy resin to the amine curing agent is 1.0:1.0-1.3 according to the ratio of the molar number of epoxy groups in the water-based cationic epoxy resin to the molar number of secondary amine groups in the curing agent.

8. The use of the method for preparing a filter material having a long-lasting positive charge over a wide pH range as claimed in claim 1, characterized in that: Filter submicron and smaller particle pollutants in water.

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