METHOD FOR PREPARING DURABLE HYDROPHILIC ULTRAFILTRATION MEMBRANE

Abstract

Provided is a method for preparing a durable hydrophilic ultrafiltration membrane. In the disclosure, a functional hydrophilic molecule is synchronously synthesized during conventional dissolution of a polymer membrane material; and a resulting casting solution (a nascent membrane) is introduced into a coagulation bath, which initiates a cross-linking reaction between the functional hydrophilic molecules to form a hydrophilic cross-linked network. A hydrophilic cross-linked interpenetrating network is formed in situ during polymer phase separation to limit movement of polymer chains and formation and growth of micelles, thereby forming a relatively uniform polymer interpenetrating network structure to obtain the durable hydrophilic ultrafiltration membrane with a relatively uniform membrane pore structure.

Claims

1. A method for preparing a durable hydrophilic ultrafiltration membrane, comprising the following steps: stirring a polymer membrane material, an active molecule A, an active molecule B, and a solvent at a constant temperature, such that a functional hydrophilic molecule is synchronously synthesized and a casting solution is obtained during dissolution of the polymer membrane material; and preparing an ultrafiltration membrane from the casting solution by dry-wet phase separation, initiating a cross-linking reaction between the active molecule A and the active molecule B by using a coagulation bath to form a cross-linked network in situ; allowing the cross-linked network and a molecular chain of the polymer membrane material to jointly form a cross-linked interpenetrating network during the dry-wet phase separation; and controlling the dry-wet phase separation by forming cross-links in situ to limit movement of polymer chains and formation and growth of micelles, thereby forming a uniform polymer interpenetrating network structure to obtain the durable hydrophilic ultrafiltration membrane with a uniform membrane pore structure; wherein the active molecule A is a molecule comprising an amino group and a siloxane group, and the active molecule B is a diglycidyl ether functional hydrophilic molecule.

2. The method of claim 1, wherein based on a total amount of the casting solution being 100%, the polymer membrane material accounts for 13 wt % to 20 wt % of a weight of the casting solution, the solvent accounts for 55 wt % to 86 wt % of the weight of the casting solution, the active molecule A accounts for 1 wt % to 10 wt % of the weight of the casting solution, and the active molecule B accounts for 1 wt % to 15 wt % of the weight of the casting solution.

3. The method of claim 1, wherein the polymer membrane material is selected from the group consisting of polyvinyl chloride (PVC), chlorinated PVC, polyvinylidene fluoride (PVDF), a PVDF-chlorotrifluoroethylene (CTFE) copolymer, polysulfone (PSF), polyethersulfone (PES), polyacrylonitrile (PAN), and a mixture of two or more thererof.

4. The method of claim 1, wherein the active molecule A is selected from the group consisting of (3-aminopropyl) trimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyldimethylmethoxysilane, 3-aminopropyldiethoxymethylsilane, diethylenetriamino propyltrimethoxysilane, N-(2-aminoethyl)-3-amino-propyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane, 3-piperazinylpropylmethyldimethoxysilane, and a mixture of two or more thererof.

5. The method of claim 1, wherein the active molecule B is selected from the group consisting of diglycidyl ether, glycerol diglycidyl ether, ethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, and a mixture of two or more thererof.

6. The method of claim 1, wherein the solvent is selected from the group consisting of N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N,N-dimethylacetamide (DMAc), and a mixture of two or more thererof.

7. The method of claim 1, wherein the stirring is conducted at the constant temperature of 30 C. to 90 C. for 2 h to 48 h.

8. The method of claim 1, wherein the coagulation bath is selected from the group consisting of an aqueous sodium hydroxide solution and an aqueous hydrogen chloride solution, the aqueous sodium hydroxide solution and the aqueous hydrogen chloride solution each have a concentration of 0.1 wt % to 30 wt %, and a temperature of the coagulation bath is controlled between 25 C. and 80 C.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0025] FIG. 1 shows a comparison of dissolution of ultrafiltration membranes with different additive amounts of active molecules in a solvent.

[0026] FIG. 2 shows a comparison of pore diameter and pore diameter distribution of the ultrafiltration membranes with different additive amounts of active molecules.

DETAILED DESCRIPTION OF THE INVENTION

[0027] In order to better understand the purpose, structure and function of the present disclosure, the method for preparing an ultrafiltration membrane based on in-situ construction of cross-linked network-assisted phase separation according to the present disclosure will be described in further detail below.

Examples 1 to 10 and Comparative Example 1

[0028] 13 wt % of a polymer membrane material, 5 wt % of an active molecule A, and 75 wt % of DMF (as a solvent) were weighed, and 7 wt % of an active molecule B was added thereto. A resulting mixture was stirred at a constant temperature of 40 C. for 48 h until completely dissolved to form a uniform solution. After membrane scraping, a resulting membrane was placed in a coagulation bath with a cross-linking factor to prepare a flat ultrafiltration membrane by phase inversion. Types of the active molecule A and the active molecule B and composition of the coagulation bath are shown in Table 1. The coagulation bath was at a temperature of 25 C.

TABLE-US-00001 TABLE 1 Effect of adding different reactive active molecules on properties of the flat membrane Water contact Water angle Flux contact after recovery Membrane Active Active Coagulation angle 300 h of rate SN material molecule A molecule B bath (*) testing (%) Comparative Control PES No addition Polyethylene Deionized 85 95 65 Example 1 Group 1 glycol water diglycidyl (pH = 7) ether Control PES 3- No addition Deionized 93 93 75 group 2 aminopropyl water triethoxysilane (pH = 7) Example 1 Experimental PES 3- Polyethylene Deionized 60 60 96 group aminopropyl glycol water triethoxysilane diglycidyl (pH = 7) ether Example 2 Experimental PES 3- Polyethylene Deionized 66 56 93 group aminopropyl glycol water dimethyl- diglycidyl (pH = 1) methoxysilane ether Example 3 Experimental PVDF 3- Diglycidyl Deionized 62 62 90 group aminopropyl ether water diethoxy- (pH = 5) methylsilane Example 4 Experimental PSF Diethylene- Diglycidyl Deionized 46 46 95 group triamino ether water propyltri- (pH = 7) methoxysilane Example 5 Experimental PVDF- N-(2- Glycerol Deionized 65 65 93 group CTFE aminoethyl)- diglycidyl water copolymer 3-amino- ether (pH = 9) propyltri- methoxysilane Example 6 Experimental Chlorinated N-(2- Glycerol Deionized 58 58 90 group PVC aminoethyl)- diglycidyl water 3-aminopropyl ether (pH = 11) methyldiethoxy- silane Example 7 Experimental PVC (3-aminopropyl) 1,6- Deionized 60 60 89 group trimethoxy- hexanediol water silane diglycidyl (pH = 13) ether Example 8 Experimental PVC (3-aminopropyl) Diethylene Deionized 65 65 89 group trimethoxy- glycol water silane diglycidyl (pH = 10) ether Example 9 Experimental PVC (3-aminopropyl) Ethylene Deionized 66 66 87 group trimethoxy- glycol water silane diglycidyl (pH = 2) ether Example 10 Experimental PAN 3-piperazinyl- Ethylene Deionized 63 63 93 group propylmethyl glycol water dimethoxysilane diglycidyl (pH = 7) ether

[0029] Table 1 shows the effects of adding different active molecules A and B to a casting solution on hydrophilicity and anti-pollution capacity of the ultrafiltration membrane. Comparative Example 1 is a control group, and Examples 1 to 10 are experimental groups. By adding a certain amount of the different active molecules A, such as the (3-aminopropyl) trimethoxysilane, the 3-aminopropyltriethoxysilane, the 3-aminopropyldimethylmethoxysilane, the 3-aminopropyldiethoxymethylsilane, the diethylenetriamino propyltrimethoxysilane, the N-(2-aminoethyl)-3-amino-propyltrimethoxysilane, the N-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane, and the 3-piperazinylpropylmethyldimethoxysilane, and the different active molecules B, such as the diglycidyl ether, the glycerol diglycidyl ether, the ethylene glycol diglycidyl ether, the 1,6-hexanediol diglycidyl ether, the polyethylene glycol diglycidyl ether, and the diethylene glycol diglycidyl ether, to the polymer membrane material such as the PVC, the chlorinated PVC, PVDF, the PVDF-CTFE copolymer, the PSF, the PES, and the PAN, excellent long-lasting hydrophilicity and anti-pollution capacity could be achieved, indicating that the method is universal.

[0030] In Example 1, a flat ultrafiltration membrane is prepared using the PES as the polymer membrane material, the 3-aminopropyltriethoxysilane as the active molecule A, and the polyethylene glycol diglycidyl ether as the active molecule B. Compared with only the active molecule A added in the control group 1 of Comparative Example 1 or only the active molecule B added in the control group 2 of Comparative Example 1, the ultrafiltration membrane obtained in Example 1 has a lower water contact angle and the water contact angle remains stable after running in pure water for 300 h. Moreover, the flux recovery rate of the ultrafiltration membrane obtained in Example 1 is also significantly improved compared with that of the control groups. It was proved that by simultaneously introducing a certain amount of the active molecule A and the active molecule B into the casting solution, the hydrophilicity of the ultrafiltration membrane is improved and lasting hydrophilicity is obtained, and the anti-pollution capacity of the ultrafiltration membrane is improved.

Examples 11 to 16

[0031] 20 wt % of PES (as the polymer membrane material), a certain amount of 3-aminopropyltriethoxysilane and ethylene glycol diglycidyl ether, and solvent as a balance were weighed (a total amount of a casting solution was maintained at 100%). The resulting weighed materials were stirred at a constant temperature of 80 C. for 24 h until completely dissolved to form a uniform solution. After membrane scraping, the membrane was placed in a coagulation bath with a cross-linking factor to prepare a flat ultrafiltration membrane by phase inversion. Additive amounts of 3-aminopropyltriethoxysilane and ethylene glycol diglycidyl ether are shown in Table 2. The coagulation bath was deionized water with pH=8.5, and the coagulation bath had a temperature of 80 C.

TABLE-US-00002 TABLE 2 Effect of additive amount of reactive active molecules on properties of a PES-based hollow fiber membrane Additive Additive Proportion of amount of 3- amount of cross- aminopropyltri ethylene glycol Water linked Flux BSA Flux ethoxysilane diglycidyl contact structure (L/m.sup.2 retention rate recovery rate SN (%) ether (%) angle () (%) h bar) (%) (%) Example 11 1 1 70 10 232.1 98.0 90 Example 12 1 5 60 15 619.1 98.9 98 Example 13 5 5 59 18 702.4 98.4 98 Example 14 5 10 55 35 934.2 98.1 98 Example 15 10 10 45 50 1,221.9 98.9 99 Example 16 10 15 45 50 1,300 98.3 99

[0032] Table 2 shows the effect of additive amounts of an active molecule A and an active molecule B on the properties of the PES-based hollow fiber ultrafiltration membrane. Examples 11 to 16 were the preparation of the ultrafiltration membranes by adding different amounts of the active molecule A and the active molecule B to the casting solution. As shown in Examples 11 and 12, Examples 13 and 14, and Examples 15 and 16, as the additive amount of the reactive active molecules increases, the proportion of the cross-linked structure in the ultrafiltration membrane increases, and the flux of the ultrafiltration membrane shows an increasing trend and maintains a stable retention rate of BSA molecules, the water contact angle is significantly reduced, and the flux recovery rate increases. It is proven that increasing the additive amount of reactive active molecules could help improve hydrophilicity, anti-pollution capacity, and filtration performance of the ultrafiltration membrane.

[0033] The dissolution of the ultrafiltration membranes obtained in Examples 11 to 16 in a solvent DMAc is shown in FIG. 1, where M0 is the ultrafiltration membrane of control group 1 without adding active molecule A, while M1, M2, M3, M4, M5, and M6 correspond to Examples 11, 12, 13, 14, 15, and 16 for comparison with the control group M0, respectively. As the additive amount of the active molecule A and the active molecule B increases, the ultrafiltration membrane gradually becomes insoluble, and an amount of insoluble residue shows an increasing trend, and an appearance of the residue also changes from flocculent to a complete membrane. This proves the successful construction of a hydrophilic cross-linked network. The pore diameter and pore diameter distribution of the ultrafiltration membranes obtained in Examples 11 to 16 are shown in FIG. 2, where M0 is the control group 1 of Comparative Example 1, while M1, M2, M3, M4, M5, and M6 correspond to Examples 11, 12, 13, 14, 15, and 16 for comparison with the control group 1 M0, respectively. After adding the active molecule A and the active molecule B, the pore size of the ultrafiltration membrane becomes more uniform from the wider distribution of M0. Moreover, the improvement in the additive amounts of the active molecule A and the active molecule B increases an average pore size of the ultrafiltration membrane while keeping a maximum pore size consistent, thus helping improve the separation efficiency of the ultrafiltration membrane. This proves that the pore size of the ultrafiltration membrane is uniform after adding the active molecule A and the active molecule B.

[0034] In the present disclosure, a functional hydrophilic molecule is synchronously synthesized and a uniform casting solution is obtained during dissolution of the polymer membrane material. Further, the casting solution is prepared by dry-wet phase separation into an ultrafiltration membrane, a cross-linking reaction between an active molecule A and an active molecule B is initiated with a coagulation bath, and cured into a membrane, namely a finished ultrafiltration membrane.

[0035] The present disclosure is described in conjunction with the examples, and those skilled in the art should know that various changes or equivalent substitutions can be made to the features and examples of the present disclosure without departing from the spirit and scope of the present disclosure. In addition, under the concept of the present disclosure, these features and examples can be modified to adapt to specific conditions and materials without departing from the spirit and scope of the present disclosure. Therefore, the present disclosure is not limited by the disclosed specific examples, and all examples falling within the scope of the claims of this application should belong to the scope of the present disclosure.