Polyacrylonitrile / nano whisker composite ultrafiltration membrane and preparation method thereof

Abstract

The present invention relates to a polyacrylonitrile / nano whisker composite ultrafiltration membrane and a preparation method thereof, the method comprising the following steps: 1, preparing bamboo shoot shell nano whiskers; 2, configuring casting liquid using bamboo shoot shell nano whiskers; 3, pouring the casting liquid on a clean and smooth glass plate, using a homemade film scraper to scrape the film evenly and steadily, so that the thickness of the casting liquid film is maintained at 150-250 microns; 4, transferring the casting liquid film to a coagulation bath, solidifying the casting liquid film by a phase inversion method, and then transferring the solidified casting liquid film to deionized water, changing deionized water every eight hours, and soaking for three days to obtain a polyacrylonitrile / nanocellulose ultrafiltration membrane. The method of the present invention is simple and convenient to operate, the addition of nano whiskers improves the hydrophilicity of the ultrafiltration membrane, and the superior high strength and Young's modulus of the nano whiskers themselves improve the strength of the ultrafiltration membrane.

Description

Technical Field

[0001] The invention relates to the field of ultrafiltration membranes, and in particular to a polyacrylonitrile / nano whisker composite ultrafiltration membrane and a preparation method thereof. Background Art

[0002] Water is an important resource in our lives, but the world is currently facing not only water shortages but also water quality issues. Membrane technology is becoming increasingly important in industrial wastewater and biomedicine due to its high efficiency, simple process, and low energy consumption. Polyacrylonitrile has good resistance to organic solvents, hydrolysis, and aging, and is often used as a raw material for membrane production. Nanocellulose has good high strength, high modulus, biodegradability, and sustainability. If nanocellulose is added to the membrane process through a reasonable method, it will bring significant changes to the hydrophilicity and mechanical properties of the ultrafiltration membrane. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a polyacrylonitrile / nano whisker composite ultrafiltration membrane and a preparation method thereof.

[0004] The technical solution of the present invention to solve the above technical problems is as follows:

[0005] The preparation method of polyacrylonitrile / nano whisker composite ultrafiltration membrane comprises the following steps:

[0006] Step 1, preparing bamboo shoot shell nano whiskers;

[0007] Step 2, placing polyacrylonitrile powder in an oven at 60-70° C. and drying for 20-25 hours, then preparing nano whiskers in N,N-dimethylacetamide solution to prepare a nano whisker solution with a mass concentration of 0.2-1%, then adding polyacrylonitrile powder with a mass fraction of 10-20% to the nano whisker solution to obtain a mixed solution, and then heating the mixed solution in a constant temperature water bath at 60° C. for 3 hours to obtain a casting solution;

[0008] Step 3, cooling and degassing the obtained casting liquid at room temperature for more than 12-14 hours, pouring the completely degassed casting liquid onto a clean and smooth glass plate at room temperature and a relative humidity of 50-60%, and scraping the film evenly and steadily with a homemade scraper to keep the thickness of the casting liquid film at 150-250 microns;

[0009] Step 4: Transfer the casting liquid membrane to a coagulation bath, coagulate the casting liquid membrane by phase inversion method, and then transfer the coagulated casting liquid membrane to deionized water. Change the deionized water every eight hours. After soaking for three days, the polyacrylonitrile / nanocellulose ultrafiltration membrane is obtained.

[0010] Furthermore, the method for preparing the bamboo shoot shell nano whiskers comprises the following steps:

[0011] Step 1.1, place the bamboo shoot shells in 40-60°C warm water for treatment and then dry, then place them in a water bath with a bath ratio of 1:40-60 and a temperature of 50-70°C for heating, and add sulfuric acid with a concentration of 1-3mL / L for treatment for 1-3h; place the treated bamboo shoot shells in a 60-80°C oven for drying;

[0012] Step 1.2, placing the bamboo shoot shells treated in the previous step into a hydrogen peroxide solution for 2-3 hours, and adding thiourea and sodium polyphosphate additives and 1-3% by mass of sodium hydroxide;

[0013] Step 1.3, placing the bamboo shoot shells treated in the previous step in dimethyl sulfoxide liquid with a bath ratio of 1:40-60, stirring at a temperature of 40-60°C, filtering with a vacuum pump and washing with deionized water until neutral, and drying in a 60-80°C oven;

[0014] Step 1.4, the bamboo shoot shells treated in the previous step are subjected to TEMPO oxidation method to prepare bamboo shoot shell cellulose nano whiskers.

[0015] Furthermore, in step 2, the concentration of the nanocellulose whisker solution is 0.6%.

[0016] Furthermore, the mass fraction of polyacrylonitrile in the mixed solution of step 3 is 15%.

[0017] The polyacrylonitrile / nano whisker composite ultrafiltration membrane is prepared by the above method.

[0018] The beneficial effects of the present invention are as follows: the method of the present invention is simple and convenient to operate, the addition of nano whiskers improves the hydrophilicity of the ultrafiltration membrane, and the superior high strength and Young's modulus of the nano whiskers themselves improve the strength of the ultrafiltration membrane. DETAILED DESCRIPTION

[0019] The principles and features of the present invention are described below. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0020] The preparation method of polyacrylonitrile / nano whisker composite ultrafiltration membrane comprises the following steps:

[0021] (1) Extraction of bamboo shoot shell fiber

[0022] The bamboo shoot shells were washed in 50°C warm water to remove the fluff and impurities on the surface, and dried in an oven for later use. The dried bamboo shoot shells were cut into small pieces (30 mm in longitudinal direction, 2×2 mm in cross section), heated in a 60°C water bath at a bath ratio of 1:40 with 2 mL / L H2SO4 for 1 h, washed with clean water at room temperature until neutral, and dried in an oven at 70°C for later use. 5 g of the treated bamboo shoot shells were boiled in a water bath with a bath ratio of 1:40, a scouring temperature of 95°C, a sodium hydroxide dosage of 18 g / L, and a hydrogen peroxide dosage of 40 mL / L for 150 min. 2 mL / L H2SO4 was used for acid washing at a bath ratio of 1:20 to neutralize the alkaline solution on the fiber surface. Finally, the bamboo shoot shell fibers were washed with clean water at room temperature until neutral and dried to obtain bamboo shoot shell fibers.

[0023] (2) Preparation of bamboo shoot shell nanowhiskers

[0024] The extracted bamboo shoot shell fiber was crushed through a 60-mesh sieve to obtain a 0.03 mm fiber powder, treated in dimethyl sulfoxide with a bath ratio of 1:30 for 6 hours at a temperature of 50°C, and then washed with a centrifuge until neutral, and the obtained sample was placed in a 70°C oven for drying. The bath ratio was 1:100, and 0.042g TEMPO, 0.6g NaBr, and a certain amount of 12% NaClO solution were added dropwise, and the pH value was adjusted to 10-11, stirred at a constant speed for 3 hours, and then 5mL of anhydrous ethanol was added to terminate the reaction when the pH value remained stable. The obtained solution was centrifuged in a centrifuge at 5000rpm for 5 minutes and washed repeatedly 5-6 times until neutral, the supernatant in the centrifuge tube was removed to obtain the precipitate, and the solid-liquid ratio was 1:150, and it was placed in a high-speed homogenizer and dispersed at 10000rpm for 10 minutes to obtain a nano whisker suspension. The nanowhiskers were placed in a freezer at -20°C for 1 day, taken out and placed in a freeze dryer, and dried for 2 days to obtain white bamboo shoot shell nanowhiskers.

[0025] (4) Preparation of polyacrylonitrile / nanocellulose ultrafiltration membrane

[0026] Place polyacrylonitrile powder in an oven at 60°C for 24 hours, then weigh a certain amount of nano whiskers and prepare them into N,N-dimethylacetamide solution with concentrations of 0%, 0.2%, 0.4%, 0.6%, 0.8%, and 1%, and ultrasonically disperse them for 30 minutes. Wait until the nanocellulose whiskers are evenly dispersed in the solvent, then add 15% polyacrylonitrile powder by mass, heat it in a constant temperature water bath at 60°C for 3 hours, and cool and degas the obtained casting liquid at room temperature for 12 hours. At room temperature, the relative humidity of the air is maintained between 50-60%. Pour the completely degassed casting liquid onto a clean and smooth glass plate, use a homemade scraper to scrape the film evenly and steadily, so that the thickness of the film is maintained at about 200 microns, quickly transfer the film to a coagulation bath, use a phase inversion method to convert the casting liquid into a film, and then transfer it to deionized water, changing it every eight hours for three days. As the content of nanocellulose gradually increased to 1%, the water flux of the ultrafiltration membrane gradually decreased from 125.88L / m2·h of pure polyacrylonitrile to 90.41L / m2·h. The addition of nanowhiskers can significantly enhance the mechanical properties of the ultrafiltration membrane. When the content of nanowhiskers increased from 0% to 1%, its Young's modulus increased from 103.60M(Pa) to 193.78M(Pa), and the tensile strength increased from 2.72M(Pa) to 3.52M(Pa). The performance of the ultrafiltration membrane was better when the content of nanowhiskers was 1%, and compared with the Young's modulus and tensile strength of pure polyacrylonitrile membrane, they increased by 87.04% and 27.9%, respectively.

[0027] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. Polyacrylonitrile / nano whisker composite ultrafiltration membrane, characterized in that: The preparation method of the polyacrylonitrile / nano whisker composite ultrafiltration membrane comprises the following steps: Step 1, preparing bamboo shoot shell nano whiskers; Step 2, placing polyacrylonitrile powder in an oven at 60-70° C. for 20-25 hours, then preparing nanowhiskers in N,N-dimethylacetamide solution to form a nanowhiskers solution with a mass concentration of 1%, then adding polyacrylonitrile powder with a mass fraction of 10-20% to the nanowhiskers solution to obtain a mixed solution, and then heating the mixed solution in a constant temperature water bath at 60° C. for 3 hours to obtain a casting solution; Step 3, cooling and degassing the obtained casting liquid at room temperature for more than 12-14 hours, pouring the completely degassed casting liquid onto a clean and smooth glass plate at room temperature and a relative humidity of 50-60%, and scraping the film evenly and steadily with a homemade scraper to keep the thickness of the casting liquid film at 150-250 microns; Step 4, transferring the casting liquid film to a coagulation bath, coagulating the casting liquid film by a phase inversion method, and then transferring the coagulated casting liquid film to deionized water, changing the deionized water every eight hours, and soaking for three days to obtain a polyacrylonitrile / nanocellulose ultrafiltration membrane; The method for preparing the bamboo shoot shell nano whiskers comprises the following steps: Step 1.1, place the bamboo shoot shell in 40-60℃ warm water for treatment and then dry it, then place it in a water bath with a bath ratio of 1:40-60 and a temperature of 50-70℃ for heating, and add sulfuric acid with a concentration of 1-3mL / L for treatment for 1-3h; place the treated bamboo shoot shell in a 60-80℃ oven for drying; Step 1.2, place the bamboo shoot shell treated in the previous step in a hydrogen peroxide solution for treatment for 2-3h, and add thiourea and sodium polyphosphate additives and sodium hydroxide with a mass fraction of 1-3%; Step 1.3, place the bamboo shoot shell treated in the previous step in dimethyl sulfoxide liquid with a bath ratio of 1:40-60, stir at a temperature of 40-60℃, filter with a vacuum pump, wash with deionized water until neutral, and place it in a 60-80℃ oven for drying; Step 1.4, use TEMPO oxidation method to prepare bamboo shoot shell nano whiskers from the bamboo shoot shell treated in the previous step.

2. The polyacrylonitrile / nano whisker composite ultrafiltration membrane according to claim 1, characterized in that: The mass fraction of polyacrylonitrile in the mixed solution of step 3 is 15%.