Preparation method of polyamide composite membrane containing cotton fiber

Abstract

The present invention relates to a method for preparing a composite membrane, and particularly to a method for preparing a polyamide composite membrane containing cotton fibers. By utilizing the characteristic that raw cotton fibers contain wax, the wax-containing cotton fibers after being treated with an oxidant are blended with a support casting solution to prepare a support, and a polyamide composite membrane is interfacially polymerized therefrom. The prepared polyamide composite membrane has a high rejection rate and a high peel strength.

Description

Technical Field

[0001] The present invention relates to a method for preparing a composite membrane, and particularly to a method for preparing a polyamide composite membrane containing cotton fibers. Background Art

[0002] Polyamide composite membranes are a kind of high-efficiency separation membrane materials, which are widely used in the fields of water treatment, food processing, biomedicine, etc. Their unique structure and properties enable them to effectively remove impurities and particulate matters in solutions, while maintaining high flux and good selectivity. With the continuous progress of technology, the application of polyamide composite membranes in separation technology is becoming more and more extensive, and they have become an indispensable important material in modern industrial and scientific research fields.

[0003] Interfacial polymerization is one of the common methods for preparing polyamide composite membranes, which requires contacting the aqueous phase and the organic phase successively on the support to undergo a polymerization reaction to form a polyamide structure. Therefore, the properties of the support are particularly important for polyamide composite membranes. There have been many existing technologies for improving the support in the prior art, and good technical effects have also been achieved. The most common technology is to add other substances on the surface of the support, such as molecular sieves, graphene, or other fine chemicals. And the addition of the above substances will inevitably lead to an increase in cost.

[0004] As a natural fiber, cotton fiber has a wide range of sources and a long history. It is taken from the fibrous material around the seeds of the cotton plant and is an indispensable raw material in the global textile industry. The naturalness of cotton fiber endows it with excellent properties such as softness, good hygroscopicity, and strong air permeability, making cotton products comfortable and skin-friendly when worn, and widely loved by consumers. More importantly, cotton is planted in many regions around the world, from warm and humid tropics to temperate climates, and the figure of cotton can be seen everywhere. This wide adaptability ensures the stable supply of cotton fiber. Therefore, it is worth studying whether cotton fiber can be applied to polyamide composite membranes to obtain high-performance membrane materials. Summary of the Invention

[0005] In view of the characteristics of cotton fiber, the present invention provides a method for preparing a polyamide composite membrane containing cotton fiber. By utilizing the characteristic that raw cotton fiber contains wax, the wax-containing cotton fiber after being treated with an oxidant is blended with the support casting solution to prepare a support, and a polyamide composite membrane is interfacially polymerized thereon.

[0006] Specifically, the present invention provides a method for preparing a polyamide composite membrane containing cotton fiber, which includes the following steps:

[0007] (1) Pretreat the raw cotton fiber to form cotton fiber with a wax content of 0.2 - 0.5 wt%, and cut the cotton fiber.

[0008] (2) Immerse the shredded cotton fibers in an oxidizing agent solution for oxidation treatment;

[0009] (3) Prepare a mixed solution containing a polymer, an additive, and a solvent, and add the oxidized cotton fibers to the mixed solution and stir evenly to form a casting solution;

[0010] (4) Prepare the above casting solution into a microfiltration membrane or an ultrafiltration membrane;

[0011] (5) Use the above microfiltration membrane or ultrafiltration membrane as a support to form a polyamide composite membrane by interfacial polymerization.

[0012] As a preferred method, the pretreatment includes one or more of alkali boiling, organic solvent extraction, and heat treatment.

[0013] As a preferred method, the length of the shredded cotton fibers is 0.5 - 2 mm, and its content in the casting solution is 2 - 8 wt%.

[0014] As a preferred method, the oxidizing agent is selected from hydrogen peroxide, sodium hypochlorite, and potassium permanganate, and the concentration is 3 - 12 wt%.

[0015] As a preferred method, the oxidation treatment time is 0.5 - 2 h.

[0016] As a preferred method, the polymer in the casting solution is one of polysulfone (PSF), polyethersulfone (PES), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), and polyvinyl alcohol (PVA), and the content is 15 - 60 wt%.

[0017] As a preferred method, the additive in the casting solution is one or more of a pore-forming agent or a surfactant, and the content is 2 - 10 wt%.

[0018] As a preferred method, the pore-forming agent is one of lithium chloride, sodium chloride, calcium chloride, and polyvinylpyrrolidone, and the surfactant is one of Tween 20, Tween 40, Tween 80, sodium dodecyl sulfate, and sodium dodecylbenzenesulfonate.

[0019] As a preferred method, the solvent in the casting solution is one of N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAC).

[0020] The support of the polyamide composite membrane prepared by the above method contains cotton fibers. The above polyamide composite membrane can be applied to technical fields such as reverse osmosis and nanofiltration.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] First, the present invention prepares a support containing cotton fibers by blending the treated cotton fibers with the support casting solution. The addition of cotton fibers not only improves the hydrophilicity of the support, making it more conducive to adsorbing aqueous monomers, but also has a lower cost compared to the nanoparticles used in the prior art.

[0023] Secondly, the cotton fibers are soaked in an oxidant. On the one hand, aldehyde groups are formed on the surface of the cotton fibers, which improves the layer bonding force between the composites by forming covalent bonds with the amino groups of the aqueous monomers. On the other hand, the oxidant treatment further reduces the wax on the cotton fibers, and the remaining wax forms hydrophobic points distributed at intervals.

[0024] In addition, the wax distributed at intervals does not adsorb aqueous monomers due to its hydrophobic effect, but adsorbs organic phase monomers during the interfacial process. As a result, interfacial polymerization occurs not only on the traditional vertical surface but also on the horizontal surface, thus improving the denseness and rejection rate of the membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is the surface SEM characterization of the polyamide composite membrane prepared in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0026] Example 1

[0027] The specific steps of the method for preparing the polyamide composite membrane containing cotton fibers in this example are as follows:

[0028] (1) Obtain cotton fibers with a wax content of 0.35 wt% by treating the raw cotton fibers, and cut the cotton fibers into fragments with an average length of about 1.2 mm;

[0029] (2) Select hydrogen peroxide with a concentration of 7 wt% as the oxidant, and immerse the cut cotton fibers in the oxidant solution for oxidation treatment for 1 h;

[0030] (3) Prepare a mixed solution containing polyethersulfone, lithium chloride, and N,N-dimethylformamide, and add the oxidized cotton fibers to the mixed solution and stir evenly to form a casting solution. The content of polyethersulfone in the casting solution is 45 wt%, the content of lithium chloride is 3 wt%, and the cotton fibers are 4 wt%, and the balance is the solvent;

[0031] (4) Cast the above casting solution on a smooth support, then quickly immerse it in a deionized water coagulation bath, and control the bath temperature at 25°C. After the membrane is completely cured, take it out of the coagulation bath, rinse it with clean water and dry it to form a support for standby.

[0032] (5) The above support was first impregnated in a 1 wt% m-phenylenediamine solution for 2 min, and then impregnated in a 0.5 wt% hexane solution of trimesoyl chloride for 60 s for interfacial polymerization reaction. After the reaction was completed, it was rinsed with clean water and dried to obtain a polyamide composite membrane containing cotton fibers (the SEM micrograph is shown in the figure).

[0033] Example 2

[0034] The specific steps for preparing the polyamide composite membrane containing cotton fibers in this example are as follows:

[0035] (1) The original cotton fibers were processed to obtain wax-free pure cotton fibers, and the cotton fibers were cut into fragments with an average length of about 1.2 mm;

[0036] (2) 7 wt% hydrogen peroxide was selected as the oxidant, and the cut cotton fibers were impregnated in the oxidant solution for oxidation treatment for 1 h;

[0037] (3) A mixed solution containing polyethersulfone, lithium chloride and N,N-dimethylformamide was prepared, and the oxidized cotton fibers were added to the mixed solution and stirred evenly to form a casting solution, where the content of polyethersulfone in the casting solution was 45 wt%, the content of lithium chloride was 3 wt%, the cotton fibers were 4 wt%, and the balance was the solvent;

[0038] (4) The above casting solution was cast on a smooth support, and then quickly immersed in a deionized water coagulation bath, and the bath temperature was controlled at 25 °C. After the membrane was completely cured, it was taken out of the coagulation bath, rinsed with clean water and dried to form a support for standby.

[0039] (5) The above support was first impregnated in a 1 wt% m-phenylenediamine solution for 2 min, and then impregnated in a 0.5 wt% hexane solution of trimesoyl chloride for 60 s for interfacial polymerization reaction. After the reaction was completed, it was rinsed with clean water and dried to obtain a polyamide composite membrane containing cotton fibers.

[0040] Example 3

[0041] The specific steps for preparing the polyamide composite membrane containing cotton fibers in this example are as follows:

[0042] (1) The original cotton fibers were processed to obtain cotton fibers with a wax content of 0.35 wt%, and the cotton fibers were cut into fragments with an average length of about 1.2 mm;

[0043] (2) A mixed solution containing polyethersulfone, lithium chloride and N,N-dimethylformamide was prepared, and the cut cotton fibers were added to the mixed solution and stirred evenly to form a casting solution, where the content of polyethersulfone in the casting solution was 45 wt%, the content of lithium chloride was 3 wt%, the cotton fibers were 4 wt%, and the balance was the solvent;

[0044] (3) Cast the above-mentioned casting solution on a smooth support, then quickly immerse it in a deionized water coagulation bath, and control the bath temperature at 25 °C. After the film is completely cured, take it out of the coagulation bath, rinse it with clean water and dry it to form a support for standby.

[0045] (4) First immerse the above-mentioned support in a 1 wt% m-phenylenediamine solution for 2 min, and then immerse it in a 0.5 wt% hexane solution of trimesoyl chloride for 60 s for interfacial polymerization reaction. After the reaction is completed, rinse it with clean water and dry it to obtain a polyamide composite membrane containing cotton fibers.

[0046] Example 4

[0047] The specific steps of the method for preparing a polyamide composite membrane containing cotton fibers in this example are as follows:

[0048] (1) Obtain cotton fibers with a wax content of 0.35 wt% by treating raw cotton fibers, and cut the cotton fibers into fragments with an average length of about 5 mm;

[0049] (2) Select 7 wt% hydrogen peroxide as the oxidant, and immerse the cut cotton fibers in the oxidant solution for oxidation treatment for 1 h;

[0050] (3) Prepare a mixed solution containing polyethersulfone, lithium chloride and N,N-dimethylformamide, and add the oxidized cotton fibers to the mixed solution and stir evenly to form a casting solution, where the content of polyethersulfone in the casting solution is 45 wt%, the content of lithium chloride is 3 wt%, the cotton fibers are 4 wt%, and the balance is the solvent;

[0051] (4) Cast the above-mentioned casting solution on a smooth support, then quickly immerse it in a deionized water coagulation bath, and control the bath temperature at 25 °C. After the film is completely cured, take it out of the coagulation bath, rinse it with clean water and dry it to form a support for standby.

[0052] (5) First immerse the above-mentioned support in a 1 wt% m-phenylenediamine solution for 2 min, and then immerse it in a 0.5 wt% hexane solution of trimesoyl chloride for 60 s for interfacial polymerization reaction. After the reaction is completed, rinse it with clean water and dry it to obtain a polyamide composite membrane containing cotton fibers.

[0053] Example 5

[0054] The specific steps of the method for preparing a polyamide composite membrane containing cotton fibers in this example are as follows:

[0055] (1) Obtain cotton fibers with a wax content of 0.8 wt% by treating raw cotton fibers, and cut the cotton fibers into fragments with an average length of about 1.2 mm;

[0056] (2)Use hydrogen peroxide with a concentration of 7 wt% as the oxidant, and immerse the shredded cotton fibers in the oxidant solution for 1 h of oxidation treatment;

[0057] (3)Prepare a mixed solution containing polyethersulfone, lithium chloride, and N,N-dimethylformamide, and add the oxidized cotton fibers to the mixed solution and stir evenly to form a casting solution. The content of polyethersulfone in the casting solution is 45 wt%, the content of lithium chloride is 3 wt%, and the cotton fibers are 4 wt%, and the balance is the solvent;

[0058] (4)Cast the above casting solution on a smooth support, then quickly immerse it in a deionized water coagulation bath, and control the bath temperature at 25 °C. After the membrane is completely cured, take it out of the coagulation bath, rinse it with clean water and dry it to form a support for standby.

[0059] (5)First immerse the above support in a 1 wt% m-phenylenediamine solution for 2 min, and then immerse it in a 0.5 wt% hexane solution of trimesoyl chloride for 60 s for interfacial polymerization reaction. After the reaction is completed, rinse it with clean water and dry it to obtain a polyamide composite membrane containing cotton fibers.

[0060] Carry out peel strength test on the polyamide composite membrane in the above examples and the membrane permeability of 2000 ppm sodium chloride aqueous solution under a pressure of 1 MPa. The results are shown in Table 1:

[0061] Table 1

[0062]

[0063] Based on the above data, it can be seen that the preparation method of the polyamide composite membrane of the present invention is beneficial to improving the rejection rate and peel strength of the membrane, and has high application potential.

[0064] Those skilled in the art can understand that under the teaching of this specification, some modifications or adjustments can be made to the present invention, and these modifications or adjustments should also be within the scope defined by the claims of the present invention.

Claims

1. A method for preparing a polyamide composite membrane containing cotton fibers, characterized in that It includes the following steps: pre-treating raw cotton fibers to form cotton fibers with a wax content of 0.2 - 0.5 wt%, and cutting the cotton fibers; impregnating the cut cotton fibers in an oxidant solution for oxidation treatment; preparing a mixed solution containing a polymer, an additive, and a solvent, and adding the oxidized cotton fibers to the mixed solution and stirring evenly to form a casting solution; preparing the above casting solution into a microfiltration membrane or an ultrafiltration membrane; using the above microfiltration membrane or ultrafiltration membrane as a support for interfacial polymerization to form a polyamide composite membrane; the length of the cut cotton fibers is 0.5 - 2 mm, and its content in the casting solution is 2 - 8 wt%; the oxidant is selected from hydrogen peroxide or potassium permanganate, with a concentration of 3 - 12 wt%; the oxidation treatment time is 0.5 - 2 h.

2. The method according to claim 1, wherein The pre-treatment includes one or more of alkali boiling, organic solvent extraction, and heat treatment.

3. The method according to claim 1, wherein The polymer in the casting solution is one of polysulfone (PSF), polyethersulfone (PES), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), and polyvinyl alcohol (PVA), with a content of 15 - 60 wt%.

4. The method according to claim 1, wherein The additive in the casting solution is one or more of a pore-forming agent or a surfactant, with a content of 2 - 10 wt%.

5. The method according to claim 4, characterized in that The pore-forming agent is one of lithium chloride, sodium chloride, calcium chloride, and polyvinylpyrrolidone, and the surfactant is one of Tween 20, Tween 40, Tween 80, sodium dodecyl sulfate, and sodium dodecylbenzenesulfonate.

6. The method according to claim 1, characterized in that The solvent in the casting solution is one of N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAC).

7. A polyamide composite membrane prepared by the method according to claim 1, characterized in that The support of the polyamide composite membrane contains cotton fibers.

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