Polyacrylonitrile fiber paper as well as preparation method and application thereof

Abstract

The invention relates to the field of specialty paper and filtration, and discloses polyacrylonitrile fiber paper as well as a preparation method and application thereof. According to the invention, polyacrylonitrile fiber is used as a raw material, the hydrophobic surface of the polyacrylonitrile fiber is changed into a hydrophilic surface through alkali treatment, uniform dispersion in water is realized, and the polyacrylonitrile fiber paper is obtained through pulping by a papermaking method, wet forming, squeezing dehydration and drying. The polyacrylonitrile fiber is subjected to alkaline hydrolysis through alkali treatment, so that the hydrophilicity of the fiber is enhanced, the prepared polypropylene fiber paper is uniform in fiber distribution, rich in functional groups on the surface of the fiber, uniform in pore structure and high in strength, can be applied to the technical fields of filtration and separation of liquid and air, battery diaphragms and the like, and solves the problem of large-scale and low-cost preparation of the polyacrylonitrile fiber paper.

Description

Technical Field

[0001] The invention relates to the field of special paper and filtration, and relates to a fiber paper and a preparation method and application thereof, and in particular to a polyacrylonitrile fiber paper and a preparation method thereof. Background Art

[0002] The important component membrane of membrane separation technology has many materials for its preparation, and polyacrylonitrile has become an excellent material for preparing ultrafiltration membrane because of its advantages such as excellent chemical stability, resistance to organic solvents and light resistance, but its hydrophilicity is poor, and long-term operation will cause the membrane to be seriously polluted, thereby shortening the service life of the membrane. Therefore, the present invention introduces different hydrophilic groups on the polyacrylonitrile membrane to increase the hydrophilicity of the polyacrylonitrile ultrafiltration membrane, and explores the performance research of polyacrylonitrile modified membrane in membrane separation. The membrane separation method mainly utilizes different membrane pore sizes to realize the screening of different components in the solution, and its driving force is the external pressure or the concentration difference on both sides of the membrane. According to the membrane pore size, the separation membrane is divided into microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) etc. Compared with traditional processes, membrane separation has many advantages, such as: (a) good effluent quality and high concentration multiple; (b) simple operation, wide adaptability, and can treat various forms of pollutants in wastewater; (c) no phase change in the treatment process, low energy consumption, reliable and stable operation; (d) system integration with various conventional treatment processes can be achieved. Although nanofiltration and reverse osmosis membranes can effectively remove small molecular organic matter and heavy metal ions, they have high operating pressure and high energy consumption, and the cost of treating low-concentration and large-volume wastewater is high. Ultrafiltration membranes have low operating pressure, low energy consumption, and low cost, but they cannot effectively intercept low molecular weight pollutants and heavy metal ions, and the selective recovery effect of useful species is poor. Affected by the membrane structure and surface properties, the permeation flux and selectivity of the separation membrane are also mutually restricted. The complex components in the water will contaminate the membrane surface, increase energy consumption and reduce the membrane life. Therefore, there are still certain restrictions on the membrane separation method in industrial wastewater treatment. Membrane or paper separation technology is a method of using membrane or paper to screen, filter, purify, etc. the target components in a mixture system based on their size. It has low energy consumption and high separation efficiency, which gives it significant advantages over traditional separation technologies.

[0003] Polyolefin membrane materials include polypropylene (PP) and polyacrylonitrile (PAN). These membrane materials have good chemical and mechanical properties. The membrane materials prepared by them are mostly used in water treatment, petrochemical industry, drug purification and sewage treatment, and have become the research object of many researchers. Due to its excellent solvent resistance, light resistance, good thermal stability and low price, polyacrylonitrile is a common material for producing separation membranes. PAN, as a vinyl polymer, is formed by the polymerization of many acrylonitrile units (AN) through free radicals. In the late 1980s, researchers conducted a systematic study on the molecular structure of polyacrylonitrile. Spectral characterization showed that AN in the polyacrylonitrile molecule is connected in the form of head-to-tail connection, and there is a strong polar -CN in the polyacrylonitrile molecule, which makes the molecules have a strong dipole effect. Since the adjacent cyano groups have the same polarity, they repel each other, so that the cyano groups are arranged at a certain angle. The strong force in the polyacrylonitrile molecule restricts the activity of the macromolecule, resulting in a regular helical structure of its main chain. The energy required for the cyano group in this conformation is minimal, and it has excellent stability. Polyacrylonitrile filter materials are widely used in the fields of separation and purification, including but not limited to the selective separation, concentration and purification of mixed fluids, such as the production of sterile water and ultrapure water, treatment and recycling of sewage, as well as applications in the fields of medical care, bioengineering, food industry, electronics industry, etc.

[0004] The most prominent problem of polyacrylonitrile membrane is that it has poor hydrophilicity, and when separating some macromolecular substances (such as proteins), it will encounter serious membrane fouling. To address this problem, the most effective method is to modify PAN appropriately so that it can effectively improve hydrophilicity, enhance separation efficiency, improve anti-pollution characteristics, prolong working time and expand application channels. Chemical modification mainly involves grafting or copolymerizing specific functionalized groups on polymer membrane materials through chemical reactions. This method can perfectly modify membrane materials from the interaction of chemical bonds and the structure of materials. Therefore, the modified polyacrylonitrile membrane has higher controllability in hydrophilicity and anti-pollution, and the operation difficulty is greatly reduced. At present, polypropylene filter materials are mainly prepared by sintering, melt extrusion, composite method, phase inversion, stretching, solution casting and spinning. However, these methods have low production efficiency, high process production cost and difficult to adjust the structure; while wet papermaking technology has the advantages of high production efficiency, flexible and adjustable components and structures of prepared filter materials, which can significantly reduce the production cost of filter materials and achieve controllable structural performance. However, due to the poor hydrophilicity of polyacrylonitrile fiber, its dispersibility in water is poor, and it is difficult to prepare paper-based filter materials with uniform fiber distribution and structure through papermaking wet process technology. Summary of the invention

[0005] The purpose of the present invention is to use alkali to chemically modify polyacrylonitrile fiber, so that its hydrophobic cyano group (-CN) undergoes alkaline hydrolysis, and a simple method is used to form hydrophilic functional groups on the surface of polyacrylonitrile fiber, so that it can be evenly dispersed in water, and then a large-scale wet papermaking process is used to prepare polyacrylonitrile fiber paper with good fiber uniformity. The polyacrylonitrile fiber paper not only has good mechanical strength, but also has a rich surface of hydrophilic functional groups such as carboxyl and amino groups, and can be applied to the field of filtration and separation, solving the problem of large-scale and low-cost preparation of polyacrylonitrile fiber paper.

[0006] The purpose of the present invention is achieved by at least one of the following technical solutions.

[0007] In order to achieve the above object, the present invention provides a method for preparing polyacrylonitrile fiber paper, which comprises the following steps:

[0008] (1) placing polyacrylonitrile fiber in an alkaline solution and stirring the solution to react, and then washing the fiber with water;

[0009] (2) beating the polyacrylonitrile fiber obtained in step (1) to obtain fibrillated fibers;

[0010] (3) The fibers treated in step (2) are placed in water and stirred to form a fiber dispersion, and the dispersion is filtered, dehydrated, pressed, and dried through a papermaking mesh to obtain polyacrylonitrile fiber paper.

[0011] Further preferably, in step (1), the polyacrylonitrile fiber has a length of 1-10 mm.

[0012] Further preferably, in step (1), the mass concentration of the alkaline solution is 0.1%-30%; and the solid-liquid ratio of the fiber to the solution is 1:100-5:1 g / mL.

[0013] Further preferably, in step (1), the alkaline solution is one or more of NaOH solution, KOH solution, and ammonia water.

[0014] Further preferably, in step (1), the alkaline solution treatment time is 0.5 minutes to 24 hours, and the treatment temperature is -10 to 100°C.

[0015] Further preferably, in step (2), the beating degree of the polyacrylonitrile fiber is 7 to 80° SR.

[0016] Further preferably, in step (3), the fiber mass concentration in the dispersion is 0.05%-3%.

[0017] Further preferably, in step (3), the drying temperature is 50-150°C.

[0018] The polyacrylonitrile fiber paper of the invention is applied to the field of filtration and separation.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The invention adopts alkali treatment to hydrophilically modify the polyacrylonitrile fiber, and makes it fibrillated by pulping, so that it can be evenly dispersed in water, ensuring the uniformity of paper sheets when papermaking on the web, and wet papermaking can reduce the manufacturing cost to the greatest extent; the prepared polyacrylonitrile fiber paper has uniform fiber and pore structure and high strength, which solves the problems of high cost of preparing polyacrylonitrile filter materials and difficult to control pore structure, and has a large number of functional groups and good hydrophilicity, and has great application prospects in the fields of adsorption, separation and filtration. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1a to Figure 1f They are the uniformity diagrams of the polyacrylonitrile papers obtained in Examples 1-6 respectively;

[0022] Figure 2 This is the uniformity diagram of the polyacrylonitrile paper obtained in Comparative Example 1;

[0023] Figure 3 This is the water contact angle diagram of the polyacrylonitrile paper obtained in Comparative Example 1;

[0024] Figure 4 This is the water contact angle diagram of the polyacrylonitrile paper obtained in Example 1;

[0025] Figure 5 The pore size and distribution diagram of the polyacrylonitrile paper obtained in Example 1;

[0026] Figure 6 Example 1 SEM image of polyacrylonitrile fiber;

[0027] Figure 7 This is a scanning electron microscope image of polyacrylonitrile fiber. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out under normal conditions. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0029] The terms used in this specification are for the purpose of describing specific embodiments only and are not intended to limit this specification. The singular forms of "a", "the" and "the" used in one or more embodiments of this specification and the appended claims are also intended to include plural forms unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used in one or more embodiments of this specification refers to and includes any or all possible combinations of one or more associated listed items.

[0030] Example 1

[0031] This embodiment provides a method for preparing polyacrylonitrile paper, the specific contents of which are as follows:

[0032] Take 25 portions of 3 mm polyacrylonitrile fibers and place them in a sodium hydroxide solution with a mass fraction of 10% at 80°C for 60 minutes. Wash the treated polyacrylonitrile fibers with deionized water until they are neutral, and place them in a pulping machine to be beaten to a beating degree of 52°SR. Figure 7 It was observed that the surface of the polyacrylonitrile fiber was obviously fibrillated, and then the treated polyacrylonitrile fiber was placed in a decomposition tank to a concentration of 0.5%, stirred and dispersed evenly, and finally put on the net to make paper, filtered and dehydrated, pressed, and dried to obtain Figure 1a Medium uniform polyacrylonitrile fiber paper, Figure 4 The medium contact angle indicates that the originally hydrophobic surface becomes hydrophilic after base treatment.

[0033] Example 2

[0034] This embodiment provides a method for preparing polyacrylonitrile paper, the specific contents of which are as follows:

[0035] Take 30 parts of 6mm polyacrylonitrile fiber and place it in a lithium hydroxide solution with a mass fraction of 15% at 75°C for 120 minutes. Wash the treated polyacrylonitrile fiber with deionized water until it is neutral, place it in a beater and beat it to a beating degree of 52°SR. Then place the treated polyacrylonitrile fiber in a decomposition tank to a concentration of 0.8%, stir and disperse it evenly, and finally put it on the net for papermaking, filter and dehydrate it, press it, and dry it to obtain Figure 1b Medium uniform polyacrylonitrile fiber paper.

[0036] Example 3

[0037] This embodiment provides a method for preparing polyacrylonitrile paper, the specific contents of which are as follows:

[0038] Take 25 parts of 10mm polyacrylonitrile fiber and place it in a potassium hydroxide solution with a mass fraction of 10% at 70°C for 180 minutes. Wash the treated polyacrylonitrile fiber with deionized water until it is neutral, place it in a beater and beat it to a beating degree of 52°SR. Then place the treated polyacrylonitrile fiber in a decomposition tank to a concentration of 0.4%, stir and disperse it evenly, and finally put it on the net to make paper, filter and dehydrate it, press it, and dry it to obtain Figure 1c Medium uniform polyacrylonitrile fiber paper.

[0039] Example 4

[0040] This embodiment provides a method for preparing polyacrylonitrile paper, the specific contents of which are as follows:

[0041] Take 22 parts of 1mm polyacrylonitrile fiber and place them in a 90°C, 15% ammonia solution for 300 minutes. Wash the treated polyacrylonitrile fiber with deionized water until it is neutral, place it in a beater and beat it to a beating degree of 52°SR. Then place the treated polyacrylonitrile fiber in a decomposition tank to a concentration of 0.5%, stir and disperse it evenly, and finally put it on the net to make paper, filter and dehydrate, press and dry it to obtain Figure 1d Medium uniform polyacrylonitrile fiber paper.

[0042] Example 5

[0043] This embodiment provides a method for preparing polyacrylonitrile paper, the specific contents of which are as follows:

[0044] Take 25 parts of 3mm polyacrylonitrile fiber and place it in 80℃, 10% by mass sodium hydroxide solution for 60min, wash the treated polyacrylonitrile fiber with deionized water until neutral, place it in a beater and beat it to a beating degree of 63°SR, then place the treated polyacrylonitrile fiber in a decomposition tank to a concentration of 0.7%, stir and disperse it evenly, and finally put it on the net to make paper, filter and dehydrate, press and dry it to obtain Figure 1e Medium uniform polyacrylonitrile fiber paper.

[0045] Example 6

[0046] This embodiment provides a method for preparing polyacrylonitrile paper, the specific contents of which are as follows:

[0047] Take 25 parts of 3mm polyacrylonitrile fiber and place it in a sodium hydroxide solution with a mass fraction of 10% at 80°C for 60 minutes. Wash the treated polyacrylonitrile fiber with deionized water until it is neutral, place it in a beater and beat it to a beating degree of 23°SR. Then place the treated polyacrylonitrile fiber in a decomposition tank to a concentration of 0.7%, stir and disperse it evenly, and finally put it on the net to make paper, filter and dehydrate it, press it, and dry it to obtain Figure 1f Medium uniform polyacrylonitrile fiber paper.

[0048] Comparative Example 1

[0049] This embodiment is different from Embodiment 1 in that no alkali treatment is performed.

[0050] Take 25 parts of 3mm polyacrylonitrile fiber and put them in a beater to beat the beating degree to 57°SR. Then put the treated polyacrylonitrile fiber in a decomposition tank to a concentration of 0.5%, stir and disperse evenly, and finally put them on the net to make paper, filter and dehydrate, press and dry to obtain polyacrylonitrile fiber paper with uniformity as shown in FIG. Figure 2 As shown, Figure 3 The contact angle of the unmodified product without alkali treatment is too large and is not suitable for membrane separation.

[0051] Test Example 1

[0052] Polyacrylonitrile paper uniformity test: Use Techpap 2D LAB F / SENSOR dust uniformity meter to test the paper uniformity. Put the paper sample on the test bench. The size of the test sample should be able to cover the test area. Press the test button to capture the paper uniformity. The uniformity of the paper is judged based on its uniformity standard deviation. The smaller the standard deviation, the better the paper uniformity.

[0053] Water contact angle test: The water contact angle (WCA) test was performed on the membrane surface using the sessile drop method at 25°C. The smaller the water contact angle, the stronger the hydrophilicity of the membrane.

[0054] Pore ​​size analysis experiment: The pore size of polyacrylonitrile paper was tested using a fully automatic gas permeation pore size analyzer, and the distribution of through-hole pore size and permeability were analyzed. The determination method is an analytical method that uses gas or liquid penetration pressure to expel fluid from the pores, and the pore size is calculated based on its related characteristics.

[0055] Scanning electron microscopy (FE-SEM, Merlin, Zeiss) was used to characterize the morphology and surface morphology of polyacrylonitrile fiber paper.

[0056] Figure 4 The water was absorbed into the polyacrylonitrile paper 0.3s after the liquid was dropped, which proved that the modified polyacrylonitrile fiber had a large number of hydrophilic functional groups and the prepared polyacrylonitrile paper had excellent hydrophilicity.

[0057] It should be understood that although the terms first, second, etc. may be used to describe various information in one or more embodiments of this specification, this information should not be limited to these terms. These terms are only used to distinguish similar objects and are not necessarily used to describe the order or sequence of features described in one or more embodiments of this specification. In addition, the terms "having" and "including" are similarly expressed to indicate a non-exclusive scope. For example, a process, method, system, product or device that includes a series of steps or modules is not necessarily limited to the contents listed in detail, but may include inherent contents related to these steps or modules that are not listed.

[0058] It should be understood that the above detailed description of the technical solution of the present invention with the help of optimized embodiments is illustrative rather than restrictive, and it cannot be determined that the specific implementation methods of the present invention are limited to this. For ordinary technicians in the technical field to which the present invention belongs, without departing from the concept of the present invention, modifications to the technical solutions recorded in the embodiments, or equivalent replacement of some of the technical features therein, should be deemed to fall within the scope of patent protection determined by the claims submitted for the present invention.

[0059] The above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing polyacrylonitrile fiber paper, characterized in that: The method comprises the following steps: (1) placing polyacrylonitrile fiber in an alkaline solution and stirring the solution to react, and then washing the fiber with water; (2) beating the polyacrylonitrile fiber obtained in step (1) to obtain fibrillated fibers; (3) The fibers treated in step (2) are placed in water and stirred to form a fiber dispersion, and the dispersion is filtered, dehydrated, pressed, and dried through a papermaking mesh to obtain polyacrylonitrile fiber paper.

2. The method for preparing polyacrylonitrile fiber paper according to claim 1, characterized in that: In step (1), the length of the polypropylene fiber is 1-10 mm.

3. The method for preparing polyacrylonitrile fiber paper according to claim 1, characterized in that: In step (1), the mass concentration of the alkaline solution is 0.1%-30%; the solid-liquid ratio of the fiber to the solution is 1:100-5:1 g / mL.

4. The method for preparing polyacrylonitrile fiber paper according to claim 1, characterized in that: In step (1), the alkaline solution is one or more of NaOH solution, KOH solution and ammonia water.

5. The method for preparing polyacrylonitrile fiber paper according to claim 1, characterized in that: In step (1), the alkaline solution treatment time is 0.5 minutes to 24 hours, and the treatment temperature is -10 to 100°C.

6. The method for preparing polyacrylonitrile fiber paper according to claim 1, characterized in that: In step (2), the beating degree of the polyacrylonitrile fiber is 7 to 80° SR.

7. The method for preparing polyacrylonitrile fiber paper according to claim 1, characterized in that: In step (3), the fiber mass concentration in the dispersion is 0.05%-3%.

8. The method for preparing polyacrylonitrile fiber paper according to claim 1, characterized in that: In step (3), the drying temperature is 50-150°C.

9. Polyacrylonitrile fiber paper prepared by the preparation method according to any one of claims 1 to 8.

10. The polyacrylonitrile fiber paper according to claim 9 is used in the field of filtration and separation.

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