GB2601027A

GB2601027A - High-strength and high-cutoff hollow fiber membrane and preparation method thereof

Info

Publication number: GB2601027A
Application number: GB2109180.6A
Authority: GB
Inventors: An Kang; Li Jianhua; Zhao Xiaoying; Zeng Xionghui; Hu Junhui
Original assignee: Aqfilm Membrane Materials Jiaxing Co Ltd; Aqfilm Membrane Mat Jiaxing Co Ltd
Current assignee: Aqfilm Membrane Materials Jiaxing Co Ltd; Aqfilm Membrane Mat Jiaxing Co Ltd
Priority date: 2020-11-12
Filing date: 2021-06-25
Publication date: 2022-05-18
Also published as: CN112316756A; GB202109180D0

Abstract

A high-strength and high-cutoff hollow fiber membrane and a preparation method thereof. The present invention adopts a thermally induced phase separation (TIPS) method to prepare a hollow fibre membrane with a fluorine-containing polymer as a substrate and polyamide as a polymer blend; where a compatibilizer is added to raw materials for the preparation of the membrane. The preparation of the membrane includes the following steps:(i) blending and granulating; (ii) spinning; and (iii) washing and shaping. The compatibilizer may be styrene-maleic anhydride copolymer SMA or styrene-ethylene oxide copolymer SEO. The prevent invention has the advantages that: (1) the preparation process is simple; and the existing TIPS technical equipment is employed only; (2) the prepared filtering membrane product has a high strength and high cutoff performance and maintains the hydrophilicity because of the recation between the compatibilizer and the polymer blend, can promote the deep purification of water.

Description

High-Strength and High-Cutoff Hollow Fiber Membrane and Preparation Method Thereof Technical Field The present invention relates to the field of membrane separation technology, and particularly relates to a high-strength and high-cutoff TIPS hollow fiber membrane and a preparation method thereof

Background

The membrane separation technology is a kind of precise separation technology developed in recent years. As a major material for the preparation of a porous membrane, a large number of polyvinylidene fluoride (PVDF) have been applied in the field of water treatment, for example, turbidity removal of slightly-polluted water on the earth's surface, pretreatment of municipal wastewater and the like. Chlorine resistance, pressure resistance, strength, cutoff performance and hydrophilia (good hydrophilia may improve the antifouling property of a membrane) are technical parameters to determine whether the porous membrane can be used for water treatment. Thermally Induced Phase Separation (TIPS) is that a polymer and a high-boiling point diluent form a polymer casting membrane solution at high temperature; when the temperature drops, the casting membrane solution is subjected to solid-liquid or liquid-liquid phase separation, and then extracted to remove diluent, where the space where the diluent occupies in the casting membrane solution forms micropores. The TIPS method may usually obtain a spherical particle structure formed by solid-liquid phase separation, a closed honeycomb pore structure formed by liquid-liquid phase separation, or a penetrating net-like pore structure formed by Spinodal decomposition. Non-solvent Induced Phase Separation (NIPS) is that a polymer and a solvent are dissolved at a certain temperature to be prepared into a homogeneous solution, and a casting membrane solution for film formation is soaked into a non-solvent; the double diffusion between the solvent and the non-solvent triggers phase separation to form an asymmetric separating membrane having a compact layer surface. The method is a kind of film making method which has been most widely used by manufacturers at home and abroad. Compared with NIPS, TIPS has the advantages of easily-controllable membrane pore structure, high film strength, good membrane chlorine resistance and good pressure resistance, and especially suitable for the preparation of a porous polymer membrane without a proper solvent at room temperature. At present, the method has been used to prepare polyvinylidene fluoride, polyethylene, polypropylene and other porous membrane. However, there are poor cutoff effect and other practical problems caused by poor hydrophilia and large pore size in the preparation of membrane by TIPS, thereby seriously influencing its application. To blend hydrophilic polymers is a simple and feasible method to improve hydrophilia, thus improving permeation flux. But, the compatibility between hydrophilic copolymers, such as, cellulose acetate (CA), polyethylene-vinyl alcohol (El/AL), polyamides (nylon, PA) and PVDF is usually poor, such that it is difficult to form a polymer solution, and an obvious interface will be formed therebetween; the weak interface not only weakens the mechanical properties of the membrane, but also produces large obvious interface pores, leading to a poor cutoff effect of a filtering membrane.

Summary

An objective of the present invention is to provide a high-strength and high-cutoff hollow fiber membrane, and a simple preparation method of such a fiber membrane, thus effectively improving the compatibility between fluorine-containing polymer and polyamide as well as and hydrophilia thereof. The improvement of compatibility can eliminate interface holes, thus improving mechanical properties and decreasing the pore size of the membrane. Moreover, the present invention improves the cutoff performance of the membrane effectively while retaining the hydrophilicity, thereby achieving the deep purification of water. Therefore, the present invention effectively solves the problems of non-durable hydrophilia and low filtering precision in the PVDF hollow fiber membrane prepared by the TIPS technology. Moreover, the preparation technology of the hollow fiber membrane can be readily matched with the commercialized TIPS preparation process, which will not increase the extra equipment and operating steps.

The present invention is implemented as follows: provided is a high-strength and high-cutoff hollow fiber membrane, and the fiber membrane is prepared by a thermally induced phase separation (TIPS) method, with a fluorine-containing polymer as a substrate and polyamide as a polymer blend; where a compatibilizer is added to raw materials for the preparation of the membrane, and the compatibilizer is a copolymer; one end of the compatibilizer is a styrene segment having a better compatibility with the fluorine-containing polymer, thereby being capable of performing physical compatibilization; another end of the compatibilizer contains an epoxy or anhydride functional group which can be reacted with an primary amino group on the polyamide terminal for compatibilization to respectively produce hydroxyl (epoxy is reacted with primary amine to generate hydroxyl) and carboxyl (anhydride is reacted with primary amine to generate carboxyl on an open-loop end thereof and an ester group on another end thereof).

The compatibilizer is a styrene-maleic anhydride copolymer SMA or styrene-ethylene oxide copolymer SEO.

A preparation method of the above hollow fiber membrane, is characterized by comprising the following steps: (i) blending and granulating: respectively measuring out 20-30 parts by mass of fluorine-containing polymer, 2-9 parts by mass of polyamide, 1-3 parts by mass of compatibilizer, 57-76.9 parts by mass of diluent and 0.1-1 part by mass of antioxidant; and fully blending the above raw materials in a mixer, and extruding a mixture thereof by an extruder, then performing cooling and granulating in the air; spinning: spinning mixture particles obtained in the step (i) by an extruder at 180°C -200°C, at a drafting rate of 10 m/min-40 m/min, firstly performing cooling in the air, then performing cooling for molding in room-temperature water; (iii) washing and shaping: soaking spinning obtained in the step (ii) by room-temperature ethyl C\I alcohol and thoroughly washing to remove the diluent, then taking out and drying the spinning in the air, and placing the spinning into an oven at 80-130°C for heating and shaping treatment o CO for 10-30 min. In The fluorine-containing polymer in the step (i) is one of a PVDF homopolymer or copolymer.

The polyamide in the step (i) is polyamide generated by condensation polymerization of diacid and diamine or polyamide generated by ring opening polymerization.

The diluent in the step (i) is a mixture of N-butyl benzenesulfonamide and triethylene glycol according to a mass ratio of 3:1.

The antioxidant in the step (i) is octadecyl 13-(3,5-di-t-butyl-4-hydroxy phenyl)propionate.

In the step (ii), after being ejected from a spinneret orifice, the extruded hollow fibrous casting membrane solution spinning travels in the air by a distance of 5-30 cm, then becomes cooled by a water bath, then becomes cured for molding, and then becomes reeled up In this present invention, based on the principle of eliminating an interface by reactive compatibilization, a compatibilizer is added to raw materials of the hollow fiber membrane prepared by TIPS; the styrene segment in the styrene-ma1eic anhydride copolymer SMA or styrene-ethylene oxide copolymer SE0 has a better compatibility with the fluorine-containing polymer. Moreover, the high-reactivity anhydride group or epoxy group may be rapidly reacted with the primary amino on the polyamide terminal to achieve compatibilization and respectively generate hydrophilic carboxyl or hydroxyl, thereby effectively improving the compatibility between PVDF and PA as well as enhancing the hydrophilia of the membrane. The elimination of interface holes can not only improve mechanical properties of the fiber membrane, but also can decrease the pore size of the membrane. Moreover, the present invention improves the cutoff performance of the membrane effectively while retaining the hydrophilicity, thereby achieving the deep purification of water. Therefore, the present invention effectively solves the problems of non-durable hydrophilia and low filtering precision in the PVDF hollow fiber membrane prepared by the TIPS technology. The prevent invention has the advantages that: (1) the preparation process is simple; high-strength products may be prepared by the hollow fiber membrane equipment prepared by the existing commercialized TIPS technology alone without any extra equipment and operating steps. (2) the prepared filtering membrane product has a high strength and high cutoff performance: during the cooling and spinning process of a casting membrane solution, the compatibilizer is reacted with the polymer blend for compatibilization, thus improving the compatibility; the improvement of the compatibility eliminates interface holes, which not only enhances the mechanical properties, but also decreases the pore size of the membrane. Moreover, the present invention improves the cutoff performance of the membrane effectively while retaining the hydrophilicity, thereby achieving the deep purification of water; (3) the polymer blend has certain hydrophilia to improve the hydrophilia of the membrane to some extent as well.

Detailed Description of the Embodiments

The present invention will be further described in combination with detailed examples, and these examples are only used for describing the present invention, but not intended to limit the claims of the present invention application

Example]:

(1) according to parts by mass, 20 parts of PVDF having a number-average molecular weight of 400,000, 2 parts of polyamide PA66 having a weight-average molecular weight of 50,000, 1 part of compatibilizer SMO containing a styrene-epoxy copolymer, 76.9 parts of diluent consisting of a mixture of N-butyl benzenesulfonamide and triethylene glycol according to a mass ratio of 3:1, and 0.1 part of antioxidant octadecyl f3-(3,5-di-t-butyl-4-hydroxy phenyl)propionate were taken. The above materials were fully mixed in a mixer and extruded by an extruder, then cooled and granulated in the air to obtain mixture particles; (2) mixture particles obtained were subjected to spinning by an extruder at 190°C, at a drafting rate of 10 m/min, cooled in the air after traveling for 5 cm, then cooled for molding in room-temperature water; (3) afterwards, the spinning was soaked by room-temperature absolute ethyl alcohol for twice and thoroughly washed for 1 h each time to remove the diluent, then the spinning was taken out and dried in the air, and the spinning was placed into an oven at 80°C for heating and shaping treatment for 10 min. Through measurement, the obtained membrane had a rupture stress of 7.1 MPa, and a pore size of 95 nm. The corresponding hollow fiber membrane unreacted for compatibilization had a rupture stress of 3.8 MPa, and a pore size of 190 nm.

Example 2:

(1) according to parts by mass, 30 parts of PVDF having a number-average molecular weight of 400,000, 9 parts of polyamide PA66 having a weight-average molecular weight of 50,000, 3 parts of compatibilizer SMO containing a styrene-epoxy copolymer, 57 parts of diluent consisting of a mixture of N-butyl benzenesulfonamide and triethylene glycol according to a mass ratio of 3:1, and 1 part of antioxidant octadecyl 0-(3,5-di-t-butyl-4-hydroxy phenyl)propionate were taken; and the above materials were fully mixed in a mixer and extruded by an extruder, then cooled and granulated in the air to obtain mixture particles; (2) mixture particles obtained were subjected to spinning by an extruder at 200°C, at a drafting rate of 20m/min, cooled in 20 cm air, then cooled for molding in room-temperature water;(3) afterwards, the spinning was soaked by room-temperature absolute ethyl alcohol for twice and thoroughly washed for 1 h each time to remove the diluent, then the spinning was taken out and dried in the air, and the spinning was placed into an oven at 80°C for heating and shaping treatment for 20 min. Through measurement, the obtained membrane had a rupture stress of 15.2 MPa, and a pore size of 28 nm The corresponding hollow fiber membrane unreacted for compatibilization had a rupture stress of 6.5 MPa, and a pore size of 123 nm

Example 3:

(1) according to parts by mass, 30 parts of PVDF having a number-average molecular weight of 400,000, 9 parts of polyamide PA6 having a weight-average molecular weight of 60,000, 3 parts of copolymer compatibilizer SMO containing styrene-epoxy, 57 parts of diluent consisting of a mixture of N-butyl benzenesulfonamide and triethylene glycol according to a mass ratio of 3:1, and 1 part of antioxidant octadecyl 3-(3,5-di-t-buty1-4-hydroxy phenyl)propionate were taken; the above materials were fully mixed in a mixer and extruded by an extmder, then cooled and granulated in the air to obtain mixture particles; (2) mixture particles obtained were subjected to spinning by an extruder at 210°C, at a drafting rate of 30m/min, cooled in 20cm air, then cooled for molding in room-temperature water; (3) afterwards, the spinning was soaked by room-temperature absolute ethyl alcohol for twice and thoroughly washed for 1 h each time to remove the diluent, then the spinning was taken out and dried in the air, and the spinning was placed into an oven at 80°C for heating and shaping treatment for 30 min. Through measurement, the obtained membrane had a rupture stress of 18.4 MPa, and a pore size of 25 nm. The corresponding hollow fiber membrane unreacted for compatibilization had a rupture stress of 6.7 MPa, and a pore size of 114 nm.

Example 4:

(1) according to parts by mass, 30 parts of PVDF having a number-average molecular weight of 400,000, 9 parts of polyamide PA6 having a weight-average molecular weight of 60,000, 3 parts of copolymer compatibilizer SMA containing styrene-anhydride, 57 parts of diluent consisting of a mixture of N-butyl benzenesulfonamide and triethylene glycol according to a mass ratio of 3:1, and 1 part of antioxidant octadecyl 13-(3,5-di-t-butyl-4-hydroxy phenyl)propionate were taken; and the above materials were fully mixed in a mixer and extruded by an extruder, then cooled and granulated in the air to obtain mixture particles;(2) mixture particles obtained were subjected to spinning by an extruder at 220°C, at a drafting rate of 30m/min, cooled in the air after traveling for 20 cm, then cooled for molding in room-temperature water; (3) afterwards, the spinning was soaked by room-temperature absolute ethyl alcohol for twice and thoroughly washed for 1 h each time to remove the diluent, then the spinning was taken out and dried in the air, and the spinning was placed into an oven at 80°C for heating and shaping treatment for 20 min. Through measurement, the obtained membrane had a rupture stress of 16.7 MPa, and a pore size of 35 nm. The corresponding hollow fiber membrane unreacted for compatibilization had a rupture stress of 6.7 MPa, and a pore size of 114 nm.

Example 5:

(1) according to parts by mass, 20 parts of PVDF-hexafluoropropylene having a weight-average molecular weight of 400,000 and a melt index of 3.5 g/1 Omin, 2 parts of polyamide PA6 having a weight-average molecular weight of 60,000, 1 part of compatibilizer SMA containing a styrene-anhydride copolymer, 76.9 parts of diluent consisting of a mixture of N-butyl benzenesulfonamide and triethylene glycol according to a mass ratio of 3:1, and 0.1 part of antioxidant octadecyl f3-(3,5-di-t-butyl-4-hydroxy phenyl)propionate were taken; and the above materials were fully mixed in a mixer and extruded by an extruder, then cooled and granulated in the air to obtain mixture particles;(2) mixture particles obtained were subjected to spinning by an extruder at 180°C, at a drafting rate of 10 m/min, cooled in the air after traveling for 5 cm, then cooled for molding in room-temperature water; (3) afterwards, the spinning was soaked by room-temperature absolute ethyl alcohol for twice and thoroughly washed for 1 h each time to remove the diluent, then the spinning was taken out and dried in the air, and the spinning was placed into an oven at 80°C for heating and shaping treatment for 10 min. Through measurement, the obtained membrane had a rupture stress of 10.2 NIPa, and a pore size of 88 nm. The corresponding hollow fiber membrane unreacted for compatibilization had a rupture stress of 3.3 IMPa, and a pore size of 128 nm.

Example 6:

(1) according to parts by mass, 30 parts of PVDF having a number-average molecular weight of 400,000, 9 parts of polyamide PA1010 having a weight-average molecular weight of 50,000, 3 parts of compatibilizer SMA containing a styrene-anhydride copolymer, 57 parts of diluent consisting f a mixture of N-butyl benzenesulfonamide and triethylene glycol according to a mass ratio of 3:1, and 1 part of antioxidant octadecyl 13-(3,5-di-t-butyl-4-hydroxy phenyl)propionate were taken, and the above materials were fully mixed in a mixer and extruded by an extruder, then cooled and granulated in the air to obtain mixture particles;(2) mixture particles obtained were subjected to spinning by an extruder at 210°C, at a drafting rate of 20 m/min, cooled in the air after traveling for 25 cm, then cooled for molding in room-temperature water, (3) afterwards, the spinning was soaked by room-temperature absolute ethyl alcohol for twice and thoroughly washed for 1 h each time to remove the diluent, then the spinning was taken out and dried in the air, and the spinning was placed into an oven at 80°C for heating and shaping treatment for 20 min. Through measurement, the obtained membrane had a rupture stress of 16.1 INIPa, and a pore size of 31 nm. The corresponding hollow fiber membrane unreacted for compatibilization had a rupture stress of 6.8 MPa, and a pore size of 117 nm.

The inventor believes that to perform reactive compatibilization and thus significantly enhance the strength and cutoff performance of the filtering membrane, the following conditions need to be satisfied: (1) one end of the compatibilizer is better compatible with PVDF, and another end thereof contains high-reactivity groups, thus ensuring the reaction within a short time and relatively even distribution in PVDF, thereby effectively achieving compatibilization, avoiding the occurrence of a region with weak mechanical properties, and eliminating interface holes. Primary amino of PA has stronger reactivity, and the styrene-ethylene oxide copolymer SE0 or styrene-maleic anhydride copolymer SMA contains high-reactivity groups and has certain compatibility with PVDF, and thus they are a proper polymer blend and compatibilizer; while CAJEVAL containing weak-reactivity hydroxyl is not suitable for being used as a polymer blend. (2) the compatibilizer and the polymer blend should be in a proper amount, or each component in the prepared polymer solution has decreased compatibility. (3) A binary mixed diluent system (capable of dissolving two polymers at high temperature) is used, and the polymer blend should be in a proper amount (a proper amount can achieve the purposes of significantly enhancing and improving hydrophilia), thus ensuring that the two polymers can be thermally dissolved by the binary mixed diluent system.

Claims

Claims 1. A high-strength and high-cutoff hollow fiber membrane, the fiber membrane being prepared by a thermally induced phase separation (TIPS) method, with a fluorine-containing polymer as a substrate and polyamide as a polymer blend, characterized in that: a compatibilizer is added to raw materials for the preparation of the membrane, and the compatibilizer is a copolymer; one end of the compatibilizer is a styrene segment which has a better compatibility with the fluorine-containing polymer, thereby being capable of performing physical compatibilization; another end of the compatibilizer contains an epoxy or anhydride functional group which can be reacted with an primary amino group on the polyamide terminal for compatibilization to respectively produce hydroxyl or carboxyl.
2. The fiber membrane according to claim 1, characterized in that: the compatibilizer is a styrene-maleic anhydride copolymer SMA or styrene-ethylene oxide copolymer SEO.
3. A preparation method of the hollow fiber membrane of claim 1 or 2, characterized by comprising the following steps: (i) blending and granulating: respectively measuring out 20-30 parts by mass of fluorine-containing polymer,2-9 parts by mass of polyamide, 1-3 parts by mass of compatibilizer, 57-76.9 parts by mass of diluent and 0.1-1 part by mass of antioxidant; and fully blending the above raw materials in a mixer, and extruding a mixture thereof by an extruder, then performing cooling and granulating in the air; (i1) spinning: spinning mixture particles obtained in the step (1) by an extruder at 180°C -200°C, at a drafting rate of 10 m/min-40 m/min, firstly performing cooling in the air, then performing cooling for molding in room-temperature water; (iii) washing and shaping-soaking spinning obtained in the step (2) by room-temperature ethyl alcohol and thoroughly washing to remove the diluent, then taking out and drying the spinning in the air, and placing the spinning into an oven at 80-130°C for heating and shaping treatment for 10-30 min.
4. The preparation method according to claim 3, characterized in that the fluorine-containing polymer in the step (i) is one of a PVDF homopolymer or copolymer.
The preparation method according to claim 3, characterized in that the polyamide in the step (i) is a polyamide generated by condensation polymerization of diacid and diamine or a polyamide generated by ring opening polymerization.
6. The preparation method according to claim 3, characterized in that the diluent in the step (i) is a mixture of N-butyl benzenesulfonami de and triethylene glycol according to a mass ratio of 3:], 7 The preparation method according to claim 3, characterized in that the antioxidant in the step (i) C\I is octadecyl f3-(. ,5 phenyl)propionate.CD8. The preparation method according to claim 3, characterized in that in the step (ii), after being 0,1 ejected from an spinneret orifice, the extruded hollow fibrous casting membrane solution spinning travels in the air by a distance of 5-30 cm, then becomes cooled by a water bath, then becomes cured for molding, and then becomes reeled up.