Preparation method of acid and alkali resistant polyimide filter material

Abstract

The application discloses a preparation method of acid and alkali resistant polyimide filter material, which comprises the following steps: preparing a phosphatized ethyl cellulose and iron composite flame-retardant coating slurry; performing single-side coating finishing on a non-woven polyimide fiber felt; and obtaining the acid and alkali resistant polyimide filter material fabric through air pyrolysis pretreatment and carbonization treatment in nitrogen. In the application, the iron-containing flame-retardant coating is used to control and catalyze the pyrolysis and carbonization process of the polyimide filter material fabric, the limited carbonization of the polyimide filter material fabric is realized, the performance of the polyimide filter material itself can be maximally reserved, the acid and alkali resistant range is widened, especially the alkali resistance is improved, and the method is suitable for industrial large-size preparation and application.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of environmental protection filter materials, and particularly relates to a preparation method of acid and alkali resistant polyimide filter material. BACKGROUND

[0002] Environmental protection filter materials are widely used in power, cement, garbage incineration, steel, metallurgy, grain and other industries, and have the functions of high-efficiency filtration and air purification. In the use of filter materials in chemical, electronic, food, pharmaceutical and other industries, the acid and alkali resistance of the filter material is very important. Because there are a large amount of acid and alkali environments in the production process of these industries, if the acid and alkali resistance of the filter material is not good, the service life of the filter material will be shortened, and even the filter material cannot be used. At the same time, the acid and alkali resistance of the filter material will also affect the filtration effect, if the acid and alkali resistance of the filter material is not good, the filtration effect will be reduced, and the expected filtration effect cannot be achieved.

[0003] Generally, the acid and alkali resistance of environmental protection filter materials depends on the material and process of the filter material. Generally speaking, filter materials with high temperature resistance such as polytetrafluoroethylene (PTFE), glass fiber (GF) and polyphenylene sulfide (PPS) have good acid and alkali resistance. Although polyimide (PI) and NOMEX fibers have good acid resistance, their alkali resistance is generally poor. Data shows that if an alkaline solution is used for cleaning during the preparation of a polyimide film, the performance of the film will easily decrease, and even fail. Polyimide is an important filter material raw material, which has excellent thermal stability, mechanical properties and chemical resistance. However, polyimide may appear degradation phenomenon in some extreme environments (such as high temperature and high acid, high temperature and high alkali), which leads to performance decrease. Therefore, it is very important to improve the acid and alkali resistance of polyimide filter material.

[0004] There are many ways to improve the acid and alkali resistance of polyimide, including changing the molecular structure, adding antioxidants, adding fillers, using cross-linking agents, and adopting appropriate post-treatment methods. Different methods can be selected and combined according to specific needs to achieve the best results. Specifically, changing the molecular structure of polyimide is achieved by adjusting the structural units such as the imide group and aromatic ring in the polyimide molecule, and controlling the polymerization reaction conditions (such as temperature, catalyst, etc.) to change the structure of the polyimide molecule, thereby improving its acid and alkali resistance. The method of adding antioxidants is that polyimide is easily oxidized and decomposed in high-temperature and high-acid and high-base environments, so adding antioxidants can effectively improve the acid and alkali resistance of polyimide. Commonly used antioxidants include sulfur compounds, benzothiazoles, phosphates, etc. The method of adding fillers is to add some highly corrosion-resistant inorganic fillers (such as aluminum oxide, silicates, etc.) or organic fillers (such as polyimide resins, etc.) to polyimide, which can effectively improve its acid and alkali resistance. Fillers can increase the surface hardness and wear resistance of polyimide, thereby reducing the corrosion of polyimide in acidic and alkaline media. The cross-linking agent method is used to improve the acid and alkali resistance of polyimide by cross-linking between polyimide molecules. The cross-linking agent can be an organic cross-linking agent or an inorganic cross-linking agent. Commonly used organic cross-linking agents include polyether diols, polyhydroxy compounds, etc., and inorganic cross-linking agents include aluminates, titanates, etc. In addition, there is also the use of appropriate post-processing methods. During the preparation process of polyimide, some residual catalysts, monomers, etc. may be left behind. These residues may affect the acid and alkali resistance of polyimide. Therefore, the use of appropriate post-processing methods, such as washing, rinsing, drying, etc., can effectively remove the residues in the polyimide, thereby improving its acid and alkali resistance.

[0005] In addition to the conventional improvement methods mentioned above, other methods, such as carbonization, can also potentially enhance a material's acid and alkali resistance. Carbonization is a process in which carbon-containing materials are heated to form carbides. Carbonization forms a layer of carbide on the material's surface, which exhibits high hardness and corrosion resistance. Therefore, carbonization can improve a material's acid and alkali resistance. Common carbonization methods include chemical vapor deposition (CVD), physical vapor deposition (PVD), plasma-enhanced CVD, and flame carbonization. These methods form a uniform carbide film on the material's surface, thereby improving its corrosion resistance. However, it is important to note that the carbonization process and results may affect other material properties. For example, carbonization may make the material more brittle, leading to a decrease in its mechanical properties. Therefore, when considering using carbonization to improve a material's acid and alkali resistance, various factors must be considered to ensure that the selected material has the appropriate performance for actual use. Summary of the Invention

[0006] This section is intended to summarize some aspects of the embodiments of the present application and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract of the specification and the title of the application in order to avoid obscuring the purpose of this section, the abstract of the specification and the title of the application, and such simplifications or omissions are not intended to limit the scope of the present application.

[0007] In view of the above and / or problems existing in the prior art, the present application is proposed.

[0008] The purpose of the present application is to provide an acid and alkali resistant polyimide environmentally friendly filter material and a preparation method thereof, which has high temperature stability, non-flammability, oxidation resistance and corrosion resistance, and can effectively filter and purify air under harsh conditions such as high temperature, high humidity, high acid and alkali degree.

[0009] The present application adopts the following technical solutions: a preparation method of acid and alkali resistant polyimide filter material, comprising,

[0010] Preparation of flame-retardant coating slurry;

[0011] Single-sided coating finishing of polyimide fiber felt fabric;

[0012] The polyimide fiber fabric coated with the flame-retardant coating is subjected to a heat treatment process to obtain a carbonized polyimide fabric;

[0013] According to GB / T 30063 "Polyimide Film Acid and Alkali Stability Test Method", the acid and alkali resistant polyimide filter fabric is obtained after acid and alkali resistance test.

[0014] As a preferred scheme of the preparation method of acid and alkali resistant polyimide filter material, the flame-retardant coating material is composed of phosphated ethyl cellulose and iron;

[0015] A certain amount of phosphated ethyl cellulose is dissolved in an ethanol solution, stirred for 120 min, and slowly added with a ferric chloride solution (0.3M), and continues to be stirred to form a coating slurry with a certain viscosity;

[0016] The content of phosphated ethyl cellulose in the above slurry is 1-5wt.%; preferably, the content of phosphated ethyl cellulose is 3wt.%

[0017] The content of 50% ethanol solution in the above slurry is 85-97wt.%; preferably, the content of ethanol solution is 91wt.%.

[0018] The amount of 0.3M ferric chloride in the above slurry is 2:1 in mass ratio to phosphated ethyl cellulose.

[0019] As a preferred embodiment of the method for preparing the acid- and alkali-resistant polyimide filter material of the present invention, the coating finishing process is as follows: the coating method adopts a scraping method;

[0020] Adjust the scraper to control the coating thickness to 50-300μm; the optimized coating thickness is 150μm.

[0021] Heat setting and drying at 80℃ for 120s.

[0022] As a preferred embodiment of the method for preparing the acid- and alkali-resistant polyimide filter material of the present invention, the heat treatment process is as follows: pre-treating the coated polyimide fabric in a high-temperature furnace at 400° C. for 30 minutes in an air atmosphere;

[0023] The pretreated polyimide fabric is placed in an atmosphere furnace and heated and carbonized in a nitrogen or low oxygen environment. The heat treatment temperature is 500-700°C and the holding time is 60 minutes. The preferred heat treatment temperature is 550°C.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The temperature and time of heat treatment of polyimide fiber are reduced by finishing with iron-containing flame retardant coating; (2) The acid and alkali resistance of polyimide fiber fabric is improved by carbonization treatment, and the pH tolerance range is widened. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort. Among them:

[0027] Figure 1 The coating slurry and coating slurry viscosity prepared in Example 1 of the present invention.

[0028] Figure 2 The mass loss rate of the fabric after heat treatment with different coating thicknesses in Example 2 of the present invention.

[0029] Figure 3 The carbonization yield and fabric breaking strength loss rate of the acid- and alkali-resistant polyimide filter material prepared in Example 3 of the present invention.

[0030] Figure 4 A scanning electron microscope image of the acid- and alkali-resistant polyimide filter fabric named PI-600 in Example 4, prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0031] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0032] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0033] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive of other embodiments.

[0034] Unless otherwise specified, the raw materials used in the examples were purchased commercially.

[0035] Example 1

[0036] To prepare 100g of slurry, weigh 1, 2, 3, 4, and 5g of phosphorylated ethyl cellulose, respectively, at a mass ratio of 1-5 wt.%, and dissolve the phosphorylated ethyl cellulose in 97, 94, 91, 88, and 15g of 50% ethanol solution, stirring until uniform. Then, slowly add 2, 4, 6, 8, and 10g of 0.3mol / L ferric chloride solution, respectively, and continue stirring for 120 minutes to prepare a 100g portion of coating slurry. The viscosity of each coating slurry was measured.

[0037] The viscosity of each sample was measured and the results were as follows: Figure 1 As shown, it can be seen that as the content of phosphorylated ethyl cellulose in the coating slurry increases, the viscosity of the slurry also increases. In the application of the present invention, polyimide fabric was coated and it was found that when the mass proportion of phosphorylated ethyl cellulose was 1wt.% and 2wt.%, the coating leaked to the lower layer of the fabric to varying degrees. The main reason is the high fluidity of the coating slurry. In order to ensure the uniformity of the subsequent heat treatment, the coating slurry needs to have good fluidity while not leaking to the lower layer of the fabric. Therefore, the fluidity of the coating slurry should not be too large. Taking all factors into consideration, a mass proportion of phosphorylated ethyl cellulose of 3wt.% is more reasonable.

[0038] Example 2

[0039] Formulation of coating slurry 500g, 3wt.% phosphated ethyl cellulose, dissolve the phosphated ethyl cellulose into 91wt.% 50% ethanol solution, stir to uniformity. Then slowly add 6wt.% 0.3mol / L ferric chloride solution respectively, and continue to stir for 120min. Coating thickness of 50, 100, 150, 200, 300μm polyimide coated fabric is prepared respectively by doctor blade method, adjusting the doctor blade. Heat setting 80℃ drying 120s, and weigh the dry weight of the coated fabric. The coated polyimide fabric is pretreated in a high temperature furnace at 400℃ for 30min in air atmosphere, cooled to room temperature, and the residual mass of the fabric after heat treatment is weighed. The mass loss rate of the fabric after heat treatment is calculated.

[0040] The calculated mass loss rate of the fabric after heat treatment of each sample is shown in Table 1, and it can be seen that increasing the thickness of the flame-retardant coating is beneficial to reducing the pyrolysis mass loss of the polyimide fabric. When the coating thickness is ≥150μm, the trend of the mass loss rate of the fabric after heat treatment slows down. Considering comprehensively, the flame-retardant coating is best controlled at 150μm. Figure 2

[0041] Example 3

[0042] Formulation of coating slurry 500g, 3wt.% phosphated ethyl cellulose, dissolve the phosphated ethyl cellulose into 91wt.% 50% ethanol solution, stir to uniformity. Then slowly add 6wt.% 0.3mol / L ferric chloride solution respectively, and continue to stir for 120min. Coating thickness of 50, 100, 150, 200, 300μm polyimide coated fabric is prepared respectively by doctor blade method, adjusting the doctor blade. Heat setting 80℃ drying 120s, and weigh the dry weight of the coated fabric. The coated polyimide fabric is pretreated in a high temperature furnace at 400℃ for 30min in air atmosphere, cooled to room temperature, and the residual mass of the fabric after heat treatment is weighed. The mass loss rate of the fabric after heat treatment is calculated.

[0043] The carbonization yield and breaking strength loss rate of the same coating and pretreated polyimide fabric treated at different carbonization temperatures are shown in Table 2. Figure 3 ​The carbonization yield of the polyimide fabric gradually decreases and the strength loss gradually increases with the increase of the carbonization temperature. When the carbonization temperature is ≤600 ℃, the decrease of the carbonization yield and the increase of the strength loss are relatively gentle, and when the carbonization temperature is >600 ℃, the carbonization yield of the product decreases sharply and the strength loss increases sharply. Based on the purpose of realizing partial carbonization of the polyimide and trying to retain the strength of the raw material and the filtering performance of various filter materials, it is not appropriate to select a too high carbonization temperature, and therefore 600 ℃ is a reasonable temperature.

[0044] Example 4

[0045] The 5 groups of carbonized polyimide fabrics prepared in Example 3 and the polyimide fabric without any treatment are respectively named PI-500, PI-550, PI-600, PI-650, PI-700 and PI-0. The polyimide samples are cut into appropriate sizes, cleaned and dried. A series of buffers with different pH values are prepared, such as pH = 2, 3, 4, 6, 5, 7, 8, 9, 10, 11, 12, 13, 14, etc. Standard buffer solution or self-made buffer solution can be used. The samples are soaked in buffers with different pH values. The polyimide samples are placed in buffers with different pH values and soaked for 24 hours. The samples are taken out and cleaned with deionized water. The samples are taken out, cleaned with deionized water and then dried. The changes of the samples are observed and recorded. Whether the surface and appearance of the samples change is observed, and the mass change and the change of the breaking strength of the samples are recorded. According to the experimental results, the pH value range that the polyimide can withstand is determined, and the performance of the samples is evaluated and analyzed. The test results are shown in Tables 1, 2 and 3, respectively.

[0046] Table 1 Mass loss rate of samples after soaking in different pH solutions

[0047]

[0048] The test results in Table 1 show that after the untreated polyimide fabric is soaked in solutions with pH = 2-14 for 24 hours, the mass loss rate is small when pH <9, and the mass loss rate gradually increases when pH >10, indicating that the acid and alkali tolerance range is pH = 2-9. Under the same conditions, after the carbonized polyimide fabric is soaked in solutions with pH = 2-14 for 24 hours, the mass loss rate is small, especially in the range of pH = 11-14, the mass loss rate is significantly smaller than that of the untreated polyimide fabric.

[0049] Table 2 Breaking strength loss rate of samples after soaking in different pH solutions

[0050]

[0051] The test results in Table 2 show that after the untreated polyimide fabric is soaked in the solution with pH = 2-14 for 24 hours, the breaking strength loss is more obvious at pH = 2-4 and pH = 10-14, and the breaking strength loss is smaller at pH = 5-9, which indicates that the acid and alkali tolerance range is pH = 5-9. Under the same conditions, after the carbonized polyimide fabric is soaked in the solution with pH = 2-14 for 24 hours, the breaking strength loss changes more gently, and the breaking strength loss rate is obviously smaller than that of the untreated polyimide fabric at pH = 2-4 and pH = 10-14, but the breaking strength loss rate caused by the increase of carbonization temperature is also very obvious.

[0052] Table 3: Dissolution state of samples after soaking in different pH solutions

[0053]

[0054]

[0055] The results in Table 3 are mainly observed by the human eye. After the untreated polyimide fabric is soaked in the solution with pH = 2-14 for 24 hours, no obvious dissolution phenomenon of the sample is observed at pH ≤ 9, partial dissolution of the sample is observed at pH = 10-12, and severe dissolution of the sample is observed at pH = 13-14, but the sample is not completely dissolved, which indicates that the acid and alkali tolerance range is pH = 2-9. Under the same conditions, after the carbonized polyimide fabric is soaked in the solution with pH = 2-14 for 24 hours, the sample is basically not dissolved, which indicates that the acid and alkali tolerance range of the carbonized polyimide fabric is pH = 2-14.

[0056] Example 5

[0057] The scanning electron microscope images of the acid and alkali resistant polyimide filter fabric PI-600 prepared in Example 3 and named in Example 4 are shown in Figure 4 The untreated polyimide fabric PI-0 and the PI-600 prepared by the method of the present application are subjected to filter performance test according to the "HJ / T 324-2006 Technical Requirements for Environmental Protection Products: Filter Material for Bag-type Dust Collector", and the test data are shown in Table 4.

[0058] Table 4: Performance indicators of filter material

[0059] Performance index PI-0 PI-600 Air permeability [m3 / (m2-s)] 12.3 13.1 Static dust removal rate (%) 96.8 97.3 Dynamic dust removal rate (%) 99.5 99.1 Filter resistance (Pa) 155 141

[0060] The results in Table 4 show that the carbonized polyimide filter material is better than or close to the untreated polyimide filter material in several filter performance indicators, which indicates that the local carbonization treatment does not affect the filtering performance of the filter material.

[0061] The application provides a preparation method of acid and alkali resistant polyimide filter material, realizes single-side flame-retardant finishing of polyimide fabric through modulation of flame-retardant coating slurry, realizes partial carbonization of polyimide through pyrolysis pretreatment and high-temperature carbonization process, and finally improves the acid and alkali resistance of polyimide. Meanwhile, based on the expandability of coating and heat treatment, high-throughput, large-size preparation and application of acid and alkali resistant polyimide filter material can be quickly and simply realized.

[0062] It should be noted that the above examples are only used to illustrate the technical solutions of the present application, not to limit it. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the present application, which should be covered by the scope of the claims of the present application.

Claims

1. A method for preparing an acid- and alkali-resistant polyimide filter material, characterized in that: include, Prepare flame retardant coating slurry; Single-side coating finishing of polyimide fiber felt fabric; The polyimide fiber fabric is finished with a flame retardant coating and then subjected to a heat treatment process to obtain a carbonized polyimide fabric; The flame retardant coating material is composed of a composite of phosphorylated ethyl cellulose and iron; A certain amount of phosphorylated ethyl cellulose was dissolved in an ethanol solution, stirred for 120 minutes, and a 0.3M ferric chloride solution was slowly added dropwise, and stirring was continued to form a coating slurry with a certain viscosity; the phosphorylated ethyl cellulose content in the slurry was 1-5 wt.%; The content of 50% ethanol solution in the above slurry is 85-97wt.%; The mass ratio of 0.3M ferric chloride to phosphorylated ethyl cellulose in the slurry is 2:1; the coating finishing process is as follows: the coating method adopts a blade coating method; Adjust the scraper to control the coating thickness to 50-300μm; Heat setting and drying at 80℃ for 120s; The heat treatment process is as follows: pre-treating the coated polyimide fabric in a high temperature furnace at 400° C. for 30 minutes in an air atmosphere; The pretreated polyimide fabric is placed in an atmosphere furnace and heated and carbonized in a nitrogen or low oxygen environment. The heat treatment temperature is 500-700° C. and the holding time is 60 minutes.

Images