POLYIMIDE COMPOSITION

Abstract

A preparation method of separation membrane is provided. First, a polyimide composition including a dissolvable polyimide, a crosslinking agent and a solvent is provided. The dissolvable polyimide is represented by formula 1:

##STR00001##

wherein B is a tetravalent organic group derived from a tetracarboxylic dianhydride containing aromatic group, A is a divalent organic group derived from a diamine containing aromatic group, A is a divalent organic group derived from a diamine containing aromatic group and carboxylic acid group, and 0.1X0.9. The crosslinking agent is an aziridine crosslinking agent, an isocyanate crosslinking agent, an epoxy crosslinking agent, a diamine crosslinking agent, or a triamine crosslinking agent. A crosslinking process is performed on the polyimide composition. The polyimide composition which has been subjected to the crosslinking process is coated on a substrate to form a polyimide membrane. A wet phase inversion process is performed on the polyimide membrane.

Claims

1. A polyimide composition, used in a preparation method of a separation membrane, comprising: a dissolvable polyimide, represented by formula 1 ##STR00026## wherein B is a tetravalent organic group derived from a tetracarboxylic dianhydride containing aromatic group, A is a divalent organic group derived from a diamine containing aromatic group, A is a divalent organic group derived from a diamine containing aromatic group and carboxylic acid group, and
0.1X0.9; a crosslinking agent, wherein the crosslinking agent is an aziridine crosslinking agent, an isocyanate crosslinking agent, an epoxy crosslinking agent, a diamine crosslinking agent, or a triamine crosslinking agent; and a solvent, wherein the preparation method of the separation membrane comprises performing a crosslinking process on the polyimide composition, and a temperature of the crosslinking process is from 15 to 35 C.

2. The polyimide composition according to claim 1, wherein B is ##STR00027## A is ##STR00028## and A is ##STR00029##

3. The polyimide composition according to claim 1, wherein B is ##STR00030## A is ##STR00031## and A is ##STR00032##

4. The polyimide composition according to claim 1, wherein the aziridine crosslinking agent comprises ##STR00033##

5. The polyimide composition according to claim 1, wherein the polyimide composition further comprises an additive, including a surfactant, a porogen or a combination thereof.

6. The polyimide composition according to claim 1, wherein the polyimide composition further comprises sorbitan monolaurate, polyoxyethylene sorbitan monolaurate, ethylene glycol, polyvinyl pyrrolidone, acetone or a combination thereof.

7. The polyimide composition according to claim 5, wherein based on a total weight of the polyimide composition, a content of the dissolvable polyimide is 5 to 25 wt %, a content of the crosslinking agent is 1 to 15 wt %, and a content of the additive is 1 to 30 wt %.

Description

EXAMPLE 1

Preparation of Dissolvable Polyimide

[0062] First, the diamine monomers BAPP and DABA were dissolved at a fixed molar ratio in an organic solvent dimethylacetamide (DMAc) or N-methylpyrrolidone (NMP). After complete dissolution, a dianhydride monomer ODPA was added for polycondensation, and a high-viscosity poly(amic acid) solution was formed, wherein the molar ratio of the monomers in reaction was BAPP:DABA:ODPA=5:5:10. Then, the poly(amic acid) was cyclized to form the dissolvable polyimide of Example 1. The dianhydride monomer was not limited to ODPA and BPDA, and the diamine monomer containing carboxylic acid group was not limited to DABA. The molar ratio of the monomers in reaction was BAPP:DABA:dianhydride monomer=5:5:10, 7:3:10 or 9:1:10.

Preparation of Polyimide Composition

[0063] 15 g of the dissolvable polyimide prepared in Example 1, 5 g of an aziridine crosslinking agent, and 80 g of the solvent NMP were added to a 100 mL flask fitted with a mechanical stirrer, and stirred for 0.5 hours at 25 C. under a nitrogen atmosphere, to uniformly mix the dissolvable polyimide of Example 1 with the aziridine crosslinking agent in the solvent NMP. In this way, the polyimide composition of Example 1 was obtained.

Preparation of Separation Membrane

[0064] The polyimide composition of Example 1 was continuously stirred and cross-linked for 8 hours at 25 C. under a nitrogen atmosphere, so as to form a mixed solution of polyimides having a cross-linked structure. Then, the mixed solution was coated onto a polypropylene nonwoven fabric (that is, the substrate) by doctor blade coating, so as to form a polyimide membrane of 200 m in thickness. Subsequently, the polyimide membrane was immediately soaked in a coagulation bath containing water (that is, the non-solvent). The polyimide was precipitated out and formed a membrane. The membrane was dried in an oven at 50 C., so as to obtain a separation membrane of Example 1.

EXAMPLE 2

Preparation of Dissolvable Polyimide

[0065] A dissolvable polyimide of Example 2 was prepared following the same preparation process as that in Example 1.

Preparation of Polyimide Composition

[0066] A polyimide composition of Example 2 was prepared following the same preparation process as that in Example 1, except that the polyimide composition of Example 2 further included ethylene glycol, and the contents of the components in the polyimide composition of Example 2 were as shown in Table 1.

Preparation of Separation Membrane

[0067] The separation membrane of Example 2 was prepared following the same preparation process as that in Example 1, except that the polyimide composition of Example 2 was used.

EXAMPLE 3

Preparation of Dissolvable Polyimide

[0068] A dissolvable polyimide of Example 3 was prepared following the same preparation process as that in Example 1.

Preparation of Polyimide Composition

[0069] A polyimide composition of Example 3 was prepared following the same preparation process as that in Example 1, except that the polyimide composition of Example 3 further included sorbitan monolaurate (Product name SPAN20, manufactured by Zhongyuan Chemical Company), and the contents of the components in the polyimide composition of Example 3 were as shown in Table 1.

Preparation of Separation Membrane

[0070] The separation membrane of Example 3 was prepared following the same preparation process as that in Example 1, except that the polyimide composition of Example 3 was used.

EXAMPLE 4

Preparation of Dissolvable Polyimide

[0071] A dissolvable polyimide of Example 4 was prepared following the same preparation process as that in Example 1.

Preparation of Polyimide Composition

[0072] A polyimide composition of Example 4 was prepared following the same preparation process as that in Example 1, except that the polyimide composition of Example 4 further included ethylene glycol and sorbitan monolaurate (Product name SPAN20, manufactured by Zhongyuan Chemical Company), and the contents of the components in the polyimide composition of Example 4 were as shown in Table 1.

Preparation of Separation Membrane

[0073] The separation membrane of Example 4 was prepared following the same preparation process as that in Example 1, except that the polyimide composition of Example 4 was used.

EXAMPLE 5

Preparation of Dissolvable Polyimide

[0074] A dissolvable polyimide of Example 5 was prepared following the same preparation process as that in Example 1.

Preparation of Polyimide Composition

[0075] 12.5 g of the dissolvable polyimide prepared in Example 5, 5 g of an aziridine crosslinking agent, 4 g of polyoxyethylene sorbitan monolaurate (Product name Tween 20, manufactured by Zhongyuan Chemical Company), 4 g of PVP (Molecular weight 360 k, manufactured by Acros Corp.) and 74.5 g of the solvent NMP were added to a 100 mL flask fitted with a mechanical stirrer, and stirred for 1 hour at 25 C. under a nitrogen atmosphere, so as to uniformly mix the dissolvable polyimide of Example 5 with the aziridine crosslinking agent, Tween 20, and PVP in the solvent NMP. In this way, the polyimide composition of Example 5 was obtained.

Preparation of Separation Membrane

[0076] The polyimide composition of Example 5 was continuously stirred and cross-linked for 8 hours at 25 C. under a nitrogen atmosphere, so as to form a mixed solution of polyimides having a cross-linked structure. Then, the mixed solution was coated onto a polypropylene nonwoven fabric (that is, the substrate) by doctor blade coating, so as to form a polyimide membrane of 200 m in thickness. Subsequently, the polyimide membrane was immediately soaked in a coagulation bath containing water (that is, the non-solvent). The polyimide was precipitated out and formed a membrane. The membrane was dried in an oven at 50 C., so as to obtain a separation membrane of Example 5.

EXAMPLE 6

Preparation of Dissolvable Polyimide

[0077] A dissolvable polyimide of Example 6 was prepared following the same preparation process as that in Example 1.

Preparation of Polyimide Composition

[0078] A polyimide composition of Example 6 was prepared following the same preparation process as that in Example 5, except that the polyimide composition of Example 6 further included acetone, and the contents of the components in the polyimide composition of Example 6 were as shown in Table 1.

Preparation of Separation Membrane

[0079] The separation membrane of Example 6 was prepared following the same preparation process as that in Example 5, except that the polyimide composition of Example 6 was used.

TABLE-US-00001 TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Dissolvable polyimide (wt %) 15 15 15 15 12.5 12.5 Aziridine crosslinking agent (wt %) 5 5 5 5 5 5 Additive Ethylene glycol (wt %) 8 8 Span 20 (wt %) 4 4 Tween 20 (wt %) 4 4 PVP (wt %) 4 4 Acetone (wt %) 15 NMP (wt %) 80 72 76 68 74.5 59.5

[0080] Then, the solvent resistance test, and the measurements of the average pore size and the pure water permeation flux were performed on the separation membranes of Examples 1-6. The above-mentioned measurements are illustrated below. The results of the average pore size and the pure water permeation flux are shown in Table 2.

<Solvent Resistance Test>

[0081] The separation membranes of Examples 1-6 were placed in the solvent NMP for 24 hours, and observed. The results show that the cross-linked separation membranes of Examples 1-6 are not back dissolved in the solvent NMP. That is, the separation membranes of Examples 1-6 have good stability against NMP.

<Measurement of Average Pore Size>

[0082] The pore size of each of the separation membranes prepared in Examples 1-6 was determined following the test standard ASTM F316, using Capillary Flow Porometer (Model no. CFP-1200-AE, manufactured by POROUS MATERIALS INC., PMI).

<Measurement of Pure Water Permeation Flux>

[0083] First, the separation membranes of Examples 1-6 were fabricated into a tubular membrane (inner diameter: 3 mm) for UF, respectively. Then, the resultant tubular membrane for UF was fitted on the tester. Next, pure water was fed to the feed side of the tester, and the tester was operated at a fixed pressure of 1 bar to determine the pure water permeation flux. During the process, the stabilization time was 1 hour, and the sampling time was 10 minutes.

TABLE-US-00002 TABLE 2 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Average pore 0.018 0.0256 0.0304 0.0248 0.05 0.05 size (m) Pure water 0.569 0.324 0.467 0.955 1.8 13.5 permeation flux (LMH)

[0084] It can be known from Table 2 that the separation membranes of Examples 1-6 all have an average pore size ranging from 0.01 to 0.1 m, and a good flux. Therefore, the separation membranes of Examples 1-6 are suitable for use in UF. In addition, a rejection coefficient test was further performed on the tubular membrane fabricated with the separation membrane of Example 6 by using a PVP 360K solution, and the rejection coefficient was up to 91%.

[0085] The present invention has been described by way of examples; however, the present invention is not limited thereto. Various changes and modifications may be made by those skilled in the art without departing from the spirit and protection scope of the present invention as defined by the appended claims.