KR101032040B1 - Novel methods to improve the membrane performances through coating the hydrophilic polymers on the hydrophobic polymeric membrane surfaces followed by the wet-crosslinking - Google Patents

Abstract

The present invention relates to a method of wet crosslinking after coating the surface of a hydrophobic polymer membrane with a hydrophilic polymer, and more particularly, one hydrophilic selected from the group consisting of polyvinyl alcohol, polyallylamine hydrochloride, and mixtures thereof. Coating a surface of the hydrophobic polymer membrane with a coating aqueous solution having a ionic strength of 0.01 to 1.0 for 30 seconds to 60 minutes, and coating the coated hydrophobic polymer membrane with glutaraldehyde or maleic anhydride. It is related with the method of improving the hydrophilicity of a hydrophobic polymer membrane including the step of immersing in aqueous solution containing and crosslinking for 10 minutes-12 hours at 15-90 degreeC.

Compared to the conventional method, the present invention has an advantage of significantly improving membrane performance through a hydrophilic polymer coating on the surface of a hydrophobic polymer membrane relatively simply.

Hydrophobic polymer, water treatment membrane, hydrophilic polymer, wet crosslinking, salt, coating time, coating temperature

Description

{Novel methods to improve the membrane performances through coating the hydrophilic polymers on the hydrophobic polymeric membrane surfaces followed by the wet-crosslinking}

The present invention relates to a method for improving the hydrophilicity of a hydrophobic separator. The present invention therefore relates to the art in the field of modifying the environment, in particular the surface of water treatment membranes. In addition, the present invention relates to a technique in the field of coating a hydrophilic polymer on the water treatment membrane, and thus relates to a technique in the field of coating a polymer.

Membrane is used in the field of water treatment and the like, the performance of which is a factor such as the morphology of the membrane including characteristics of symmetry, pore shape, pore size, etc. Determined by the method or the like.

Based on these characteristics, the membrane may be classified into microfiltration, ultrafiltration, and reverse osmosis membrane. Microfiltration is a process driven by pressure and is distinguished by the size of particles or molecules that the membrane can pass through. Such microfiltration can remove very fine colloidal particles in the micrometer and submicrometer ranges. In general, microfiltration can filter small particles up to 0.05 μm, while ultrafiltration can have particles as small or smaller than 0.01 μm. Reverse osmosis works on a smaller scale.

In addition to the microstructures described above, the chemical properties of the membrane, in particular the balance of the hydrophilicity / hydrophobicity of the membrane, are very important.

Hydrophobic is defined as "dislike water", many of which are hydrophobic polymers used to cast porous membranes. Water can be penetrated by using sufficient pressure on such hydrophobic membranes, but the required pressure is very high (150-300 psi), which may damage the membrane, and the initial permeability is low, so that it takes a long time to normal permeation. It is not evenly wetted and there are many difficulties in storage.

Hydrophobic microporous membranes are typically characterized by chemical resistance, biocompatibility, low swellability and good separation performance. However, when used in the field of water treatment, hydrophobic membranes must be "hydrophilised" or "wet out" to allow permeation of water. Such hydrophilization or wetting methods may include filling an agent, such as glycerol, but some hydrophilic materials may be applied to microfiltration and ultrafiltration membranes that require mechanical strength and thermal stability because water molecules may act as plasticizers. Inappropriate.

In order to improve the hydrophilicity of the hydrophobic membrane described above, the surface of the hydrophobic polymer should be hydrophilized. A simple method for this is to blend the hydrophilic polymer with the hydrophobic polymer. PVDF (Polyvinyliden fluoride: polyvinylidene fluoride) which introduce | transduced a hydrophilic copolymer in order to provide hydrophilicity to a film | membrane is typical. In addition, hydrophilic polymers used may include cellulose acetate, sulfonated polymers, polyethylene glycols, poly (vinylpyrrolidone) (PVP), and the like. These copolymers impart some degree of hydrophilicity to the hydrophobic membrane to improve the performance of the membrane. However, depending on the degree of polymerization, the hydrophilic component may be leached from the film with time and two or more polymers are used during film formation, which causes a lot of difficulties. Hydrophilic polymers, in particular PVP, tend to slowly wash away from the membrane over time.

In addition, in the case of hydrophilization by plasma, in terms of practical technology, hydrophilization into internal pores is quite difficult, and due to the problem of high cost, actual commercialization is difficult.

In the present invention, when the hydrophobic membrane is used, the problem of water permeability and initial storage process and the problem of deterioration of the membrane performance due to washing out of the hydrophilic polymer from the blended membrane are solved.

       In addition, by providing a hydrophilicity to provide a method of improving the performance of the membrane by increasing more than the conventional water permeability,

The present invention seeks to provide a novel method for improving the hydrophilicity of a hydrophobic polymer used as a water treatment membrane by a relatively simple method.

The present invention to solve the above problems
Polyvinyl alcohol, polyallylamine hydrochloride and mixtures thereof, including one hydrophilic polymer selected from the group consisting of a salt for adjusting the ionic strength, the coating solution having an ionic strength of 0.01 ~ 1.0 to the surface of the hydrophobic polymer membrane 30 seconds to Coating for 60 minutes,
Immersing the coated hydrophobic polymer film in an aqueous solution containing glutaraldehyde or maleic anhydride and crosslinking at 15 to 90 ° C. for 10 minutes to 12 hours.
Provided is a method of improving the hydrophilicity of a hydrophobic polymer membrane.

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According to the coating method of the present invention, the hydrophilicity of the hydrophobic polymer can be significantly improved, and the hydrophilicity of the hydrophilic polymer can be prevented from decreasing over time, thereby improving the performance of the membrane.

The hydrophobic polymer used in the present invention corresponds to a polymer membrane widely used in water treatment membranes, preferably PVDF (polyvinylidene fluoride), PSf (polysulfone), PES (polyethersulfone), PEI (polyetherimide) ), PI (polyimide), PE (polyethylene), PP (polypropylene), PAmide (polyamide). In order to impart a hydrophilic group to the surface of the hydrophobic polymer as described above, a hydrophilic polymer such as PVA (polyvinyl alcohol) and PAAm (polyallylamine hydrochloride) is coated. In addition, the coating degree is controlled by changing the temperature of the coating process, changing the concentration of the coating solution, changing the ionic strength, and changing the coating time according to the end use purpose and ease of coating of the coating target film.

In the coating process using the present invention, if the concentration of the coating solution is 50ppm or less, the uniformity of the coating is reduced due to the low concentration, and the performance of the target film does not appear uniformly. Small areas of pores on the surface may disappear, causing performance degradation.

In the present invention, a salt that plays a role of ionic strength control uses conventional NaCl, LiCl, KCl, CaCl ₂ , MgCl _2, etc., which is easily decomposed in water and induces precipitation of hydrophilic polymer dissolved in water in the coating process. do. Ionic strength follows the following equation (1).

            (One)

상기한 염들의 이온세기는 코팅용액의 농도와 관련해서 조절한다. 이온세기의 증감을 통해 코팅용액 중의 용질의 석출양의 조절을 하는데, 바람직하게는 상기 이온세기는 코팅용액농도가 50~30,000ppm일 경우 0.01~1.0까지의 범위 내에서 적절히 조절하도록 한다.

The ionic strength of the salts described above is controlled in relation to the concentration of the coating solution. The precipitation amount of the solute in the coating solution is controlled by increasing or decreasing the ionic strength. Preferably, the ionic strength is appropriately adjusted within the range of 0.01 to 1.0 when the coating solution concentration is 50 to 30,000 ppm.

Meanwhile, in the present invention, the coating time should be appropriately changed in order to uniformly coat, preferably 30 seconds to 60 minutes is appropriate, but is not necessarily limited thereto.

Wet crosslinking in the present invention adds stability to the coated film as a post-treatment process after coating. In the case of wet crosslinking, the coating material is immersed in a suitable concentration of Glutaric anhydride or Maleic aldehyde solution at a temperature of 15 ~ 90 ℃ for a certain time to enhance the water resistance of the coating material.

Hereinafter, the present invention will be described in more detail with reference to Examples and drawings. The present invention will be described in more detail with reference to the following examples.

<Example 1.>

100g of PVA solution having a concentration of 150ppm was prepared to maintain Ionic Strength 0.15, and 0.15m (8.756g _{[NaC] l} / Kg _[PVA] ) of NaCl was added and completely dissolved, followed by PE dense film Glutaric prepared in a concentration of 1.25wt.% With water after dipping (2cm X 4cm X 20㎛) into solution and changing the coating time at 10 ~ 60 minutes at room temperature (about 24 ± 1 ℃). The solution was again immersed in anhydride solution and wet crosslinked at 40 ° C. for 12 hours, and the membrane was dried at room temperature. Thus, in order to observe the physical change of the film according to the coating time was carried out by measuring the contact angle to water and the results are shown in Table 1.

Table 1: Change of contact angle after PVA coating of PE film

Time
(min) 0 10 20 30 40 50 60 Angle
(degree) 90.4 42.7 42.3 43.7 41.3 41.7 39.3

The inherent PE film (coating time '0 min' in Table 1) shows a contact angle for water of 90.4 ° and about 41 ° for PVA film. On the contrary, in the case of the present invention, as shown in Table 1, the contact angle change result shows that the contact angle is almost similar to that of the inherent PVA after 10 minutes of coating time. The change in contact angle over time is shown graphically in FIG.

<Example 2>

100 g of PVA solution having a concentration of 300 ppm was prepared and dissolved in 0.15 m (8.756 g _{[NaC] l} / Kg _[PVA] ) of NaCl to a solution prepared to maintain Ionic Strength 0.15, and then completely dissolved in a PVDF dense film. (2cm X 4cm X 25㎛) was immersed in the solution to change the coating time at room temperature (about 24 ± 1 ℃) to 10 ~ 120 minutes, then taken out in a solution of Glutaric anhydride prepared at a concentration of 1.25wt.% With water After re-immersion, wet crosslinking was performed at 40 ° C. for 12 hours, and the membrane was dried at room temperature.

As another example, the hydrophilic coating solution was added in the same manner as in Example 2 by adding PAA instead of PVA. The results are shown in Table 2. The change in contact angle over time is shown graphically in FIG.

[Table 2: Change of contact angle after PVA and PAAm coating of PVDF film]

Base
polymer Coating solution Polymer PVDF PVA PAAm Soaking
time (min) 0 10 20 30 45 120 10 20 30 45 120 Contact
angle (°) 78 57 50.6 44.5 42.6 43 53 45 41 42 41

<Example 3>

100g of PVA solution having a concentration of 300ppm was prepared to maintain Ionic Strength 0.15, and 0.15m (8.756g _{[NaC] l} / Kg _[PVA] ) of NaCl was added to dissolve completely, followed by PSf dense film (2cm X 4cm X 25㎛) was immersed in the solution, coated at room temperature (about 24 ± 1 ℃) for 120 minutes, then changed, taken out, and re-immersed in Glutaric acid solution prepared with a concentration of 1.25wt.% With water The wet crosslinking was carried out at 40 ° C. for 12 hours, and the membrane was dried at room temperature.

The change of contact angle was observed by repeating the coating and wet crosslinking five times as described above, and the results are shown in Table 3 and FIG. 3.

[Table 3: Contact angle according to the number of times of PVA coating on the PSf film surface]

Number of coatings 0 One 2 5 Contact
angle (°) 66.25 42.25 40.4 41.7

As confirmed in Table 3 and FIG. 3, the effect of the coating frequency on the contact angle was reported to be insignificant.

<Example 4>

100 g of PVA solution having a concentration of 150 and 300 ppm, respectively, was prepared to maintain Ionic Strength 0.15, and then completely dissolved by adding 0.15 m (8.756 g _{[NaC] l} / Kg _[PVA] ) of NaCl. PVDF MF flat membrane (5cm X 5cm) was immersed in the solution, coated at room temperature (about 24 ± 1 ℃) for 20 minutes, then changed and taken out and re-immersed in Glutaric anhydride solution prepared at a concentration of 1.25wt.% With water. The wet crosslinking was carried out at 40 ° C. for 12 hours, and the membrane was dried at room temperature.

In addition, the change of water permeability according to the operation temperature of the surface-coated membrane was observed by using PAAm instead of PVA as a hydrophilic polymer, and the results are shown in Table 4 and FIG. 4.

In particular, when PAAm is used as a hydrophilic polymer instead of PVA, and when a cotan is formed of a mixture thereof, PAAm has an anion, and thus, it can be used as an anion exchange membrane.

Table 4: Changes in Water Permeability According to PVDF Surface Coatings

Membranes PVDF PVA (150 ppm) PVA (300 ppm) PAAm (150 ppm) PAAm (300 ppm)
Permeation
(LMH) 15 ℃ 251.4 304.41 335.46 310.10 351.35 25 ℃ 337.18 380.43 453.25 402.77 491.24 45 ℃ 458.36 539.36 542.55 532.02 563.20

In Example 4, when the coating was performed at a low concentration and a short time for the surface area of the coating object, a hydrophilic coating was applied to the top layer of the membrane to increase the permeability to water without affecting the penetration channel inside the membrane of water. It was found to indicate. The high concentration of coating solution and prolongation of coating time can cause clogging of the permeation channel of water even though the surface is hydrophilized because the surface pores of the membrane are closed, but it is not possible to control by changing these factors (coating concentration / time). It can be seen that it is possible.

1 is a view showing a change in contact angle over time after coating the PE film surface with PVA.

2 is a view showing a change in contact angle over time after PVA and PAAm coating the surface of the PVDF film.

3 is a view showing a change in contact angle that appears when the number of coating the PSf film surface using PVA.

4 is a view showing the change in water permeability when the PVDF surface is coated with PVA and PAAm.

Claims (4)

It contains one hydrophilic polymer selected from the group consisting of polyvinyl alcohol, polyallylamine hydrochloride and mixtures thereof, and a salt for adjusting the ionic strength, and the surface of the hydrophobic polymer membrane is coated with an aqueous solution having a ionic strength of 0.01 to 1.0 for 30 seconds. Coating for about 60 minutes, Immersing the coated hydrophobic polymer film in an aqueous solution containing glutaraldehyde or maleic anhydride and crosslinking at 15 to 90 ° C. for 10 minutes to 12 hours. A method of improving the hydrophilicity of the hydrophobic polymer membrane, comprising. The method of claim 1, Wherein said hydrophobic polymer membrane is one material selected from the group consisting of polyvinylidene fluoride, polysulfone, polyethersulfone, polyetherimide, polyimide, polyethylene, polypropylene and polyamide. The method of claim 1, The ion intensity control salt is one method selected from the group consisting of NaCl, LiCl, KCl, CaCl ₂ , and MgCl ₂ . delete

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