A kind of preparation method of surface self-cleaning polymer porous membrane
Technical field
The present invention relates to a kind of preparation method of perforated membrane, more specifically to a kind of preparation method of surface self-cleaning polymer porous membrane.
Background technology
Advantages such as membrane separation technique has low energy consumption, process is simple, separative efficiency is high, free from environmental pollution are the important new and high technologies that solves the energy, resource and the environmental problem in the present age, and it uses the fields such as chemical industry, food, medicine, biochemistry, environmental protection of having developed into.Polymeric material is because characteristics such as function admirable, inexpensive, easy processing have been widely used in preparing porous diffusion barrier.But, can produce two problems during application in aqueous phase separation systems such as water treatment, biology, food because surface of polymer material has hydrophobicity more: the one, the mass transfer driving force is high, and energy consumption is big; The 2nd, very easily adsorb hydrophobic organic compound and cause that film pollutes, cause membrane flux to descend, shorten membrane lifetime.Through surface modification, the preparation surface is difficult for polluting or the easy polymer porous film that cleans is to solve the effective way that film pollutes.
In recent years, the self-cleaning property Research on surface has caused common attention and has obtained important progress.The surface of a lot of plants of occurring in nature, animal has automatically cleaning character, can clean through rain drop erosion such as lotus leaf surface, and gecko is not cleaned foot pad specially can keep the adhesive force with wall, and this is the biological long-term result who adapts to nature.The surface texture of imitation lotus leaf, cicada's wings is constructed the little lug structure and the hydrophobic ingredient of micro/nano level at material surface, can give the hydrophobic self-cleaning property of material surface.Its principle is that material surface has super-hydrophobicity and very little water roll angle, and the pollutant that adheres to is easy to along with the rolling of water droplet by rolling off.Yet this automatically cleaning mechanism also is not suitable for the automatically cleaning modification of porous separation membrane surface, because water is difficult for seeing through the micro channel of surface hydrophobic perforated membrane.Utilize TiO
2The UV catalytic property also be the effective ways on design self-cleaning property surface.Under the UV irradiation, TiO
2The oxidable decomposing organic matter of particle, surface conversion is a Superhydrophilic simultaneously.With TiO
2The stain resistance on film surface, the growth that the raising water flux also can suppress bacterium can be improved in particle modified polymer porous film surface.But TiO
2/ UV method also can cause degraded, the efflorescence of matrix polymer, simultaneously TiO
2The photocatalysis efficiency of/UV method also needs further to improve.
In addition, in recent years, the surperficial automatically cleaning mechanism and the performance study of stimulation-response type polymer begin to cause concern.So-called stimulation-response is meant material after the stimulation of accepting ambient signal, and the structure of its molecule, energy state change and make the process of response.Stimulation-response type polymer can be accepted the ambient signal of temperature, pH value, ion, solvent, chemical substance, electric field, light etc.; And the variation of behaviors such as the stretching, extension of strand/curl, hydrophilic/hydrophobic, specific adsorption takes place, stimulation-respondent behavior generally has invertibity.Because polymeric material has the multiplet level, is easy to realize through molecule and structural design this intelligent performance of material.
(Advanced Materials such as Youngblood in 2007; 19; 3838-3843,2007) on substrate of glass keyed jointing have polyethylene glycol-perfluoro alkane block polymer brush of solvent stimulation-response, hydrophobic perfluoro alkane section is stretched to the outside in the oiliness environment; The structure of polymer brush counter-rotating when contacting with water, the polyethylene glycol section is stretched to the outside.Utilize the stimulation-response behavior of this solvent can realize surface self-cleaning, when the polymer brush surface that hexadecane pollutes in advance contacted also simple concussion with water after, hexadecane promptly broke away from and floats on the surface of water from the surface.The contact angle data show; The receding angle of polymer brush surface hexadecane is greater than the advancing angle of water; Youngblood thinks the gap of this contact angle just, makes water be easy at the polymer brush surface spreading and has replaced the interface of hexadecane/polymer brush, has given the self-cleaning performance of modified surface.
The gathering of temperature sensitive property (N-NIPA) (being called for short PNIPAAm) is to obtain paying close attention to maximum stimulation-response type polymers.Near its lower critical solution temperature (LCST, 32 ℃), because the variation of interactivelies such as the hydrogen bond between the PNIPAAm/ water, close and distant water, the PNIPAAm strand can stretch/curl phenomenons such as reaching the hydrophilic/hydrophobic transformation.Utilize this volume phase property of transition of PNIPAAm, (The Fourth Conference of Aseanian Membrane Society, August 16-18,2007, Taipei such as Huang Jian in 2007; Desalination, 234,42-45,2008) the alternating temperature automatically cleaning behavior on PNIPAAm surface is explored.For the PNIPAAm grafted polyethylene perforated membrane of protein contamination, be cleansing medium with water, (35 ℃/25 ℃) can make the water flux of modified porous film return to 97.5% with simple alternating temperature cleaning method near the LCST of PNIPAAm.But since LCST when above PNIPAAm have hydrophobicity, be prone to cause the pollution of protein, also difficult simultaneously a small amount of protein of remained on surface is removed fully.For stretching, extension/curling transformation of stressing the PNIPAAm strand to self-cleaning effect; (Chemical Communications such as Dai in 2008; 163-165; 2008) PNIPAAm is embedded in the slit of carbon nano pipe array, find that near the alternating temperature cleaning of LCST (45 ℃/25 ℃) can make surface contaminant gold nano particulate desorption.Adopt similarly mechanism; Yu Sanchuan etc. (publication number CN 101530751A) disclose a kind of preparation method of self-cleaning type reverse osmosis membrane in 2009; PNIPAAm has been coated in the surface of reverse osmosis membrane; Carry out surface contamination with humic acid in the time of 20 ℃, clean with water under 60 ℃, the recovery rate of modification reverse osmosis membrane water flux reaches 96.2%~98.3% as a result.
Above-mentioned employing temperature-sensitive macromolecular designs, prepares the method for self-cleaning surface, all is the volume phase property of transition that utilized PNIPAAm, i.e. near the stretching, extension of the PNIPAAm strand LCST/curl or the hydrophilic/hydrophobic transformation.Though modified surface can be realized significantly automatically cleaning effect, has ignored the surface hydrophobic that PNIPAAm has more than LCST, and the surface that this hydrophobicity causes is prone to contaminative and is difficult for cleaning.Therefore be necessary the in addition modification of the PNIPAAm molecular chain structure of temperature sensitive property; Develop a kind of novel surface self-cleaning polymer porous membrane; Can make full use of the stretching, extension/motion of curling of strand in its volume phase transition process; With and surface hydrophilicity below the LCST to the self-cleaning contribution in surface, the adverse effect that can avoid the surface hydrophobic of the above PNIPAAm strand of LCST to bring again, that further improves the PNIPAAm modified surface is difficult for contaminative and self-cleaning property.
Summary of the invention
The present invention is directed to prior art problems with not enough; A kind of preparation method of surface self-cleaning polymer porous membrane is disclosed; A kind of new type of polymer porous film surface automatically cleaning solution has been proposed promptly: on the polyalcohol stephanoporate film surface grafting temperature sensitive property gather (N-NIPA) (PNIPAAm), on the PNIPAAm grafted chain, connect hydrophilic polyethylene glycol side chain then.The introducing of hydrophilic side-chains; Overcome the easy contaminative in surface that the hydrophobicity of PNIPAAm more than lower critical solution temperature (LCST) causes; Utilize the surface hydrophilicity of PNIPAAm when LCST is following simultaneously; And the stretching, extension/curl to change the mechanical force that is provided of PNIPAAm strand in volume phase transition process, that has realized polymer-modified porous film surface is difficult for contaminative and self-cleaning property.
According to the Surface Physical Chemistry principle, the removal of greasy dirt realizes that through the mechanism of crispaturaing this moment, the Young equation can be expressed as cos θ=(γ
SW-γ
SO)/γ
WO, θ is the contact angle of greasy dirt at the surface of solids in the formula, γ
SW, γ
SOAnd γ
WOBe respectively the interfacial tension between solid-water, solid-You Heshui-oil.When θ was 180 °, greasy dirt was the spontaneous disengaging surface of solids, if 90 °<θ<180 °, greasy dirt can not spontaneously break away from the surface of solids, but can remove down the auxiliary of mechanical force.For hydrophilic surface, because γ
SWReduce, θ should be between 90 °~180 °, and this promptly is the reason that hydrophilic surface is difficult for polluting or being prone to cleaning.PNIPAAm is hydrophily in the surface when LCST is following, and the stretching, extension/curl to change the mechanical force that is provided of PNIPAAm strand in volume phase transition process, makes to utilize PNIPAAm to design self-cleaning surface to become possibility.
The present invention realizes through following technical scheme:
The preparation method of surface self-cleaning polymer porous membrane of the present invention is: the at first PNIPAAm of temperature sensitive property on the polyalcohol stephanoporate film surface grafting, hydrophilic polyethylene glycol side chain in grafting on the PNIPAAm strand then.Specifically be with the Ar method of plasma processing,, and then cause N-NIPA (being called for short NIPAAm) and carry out surface grafting polymerization at the outer surface and the fenestra inwall generation free radical of polymer porous film.Mainly be the reversible volume phase property of transition that utilizes porous film surface PNIPAAm grafted chain,, and under the acting in conjunction of the mechanical force that is provided in the strand stretching, extension/curly course, promote the disengaging of grafted pollutant promptly at its surface hydrophilicity below LCST.Yet, under hydrophobic (curling) state of PNIPAAm, be prone to cause the pollutant surface adhesion and be difficult for cleaning.For the adverse effect of this hydrophobic state that overcomes the above PNIPAAm of LCST, utilize the method for chemical grafting on the PNIPAAm grafted chain, to connect hydrophilic polyethylene glycol side chain again.Because the hydrophilic polyglycol side chain is not and NIPAAm random copolymerization so can't obviously influence the volume phase property of transition of PNIPAAm, to comprise its LCST.The introducing of hydrophilic polyglycol side chain; Make modified porous film surface in the alternating temperature cleaning process, can remain hydrophily; Overcome the easy contaminative in surface that the hydrophobicity of PNIPAAm more than LCST causes; Can utilize again simultaneously the PNIPAAm grafted chain in volume phase transition process stretching, extension/curling changes the effect of the mechanical force that is provided, that has realized polymer-modified porous film surface is difficult for contaminative and self-cleaning property.Clean carrying out alternating temperature near the water of modified porous film temperature LCST, can reach surperficial self-cleaning purpose.
The preparation method of surface self-cleaning polymer porous membrane of the present invention may further comprise the steps:
A) under the condition of starvation; To pass through polymer porous film that the surface cause to produce free radical and be immersed in and contain in the aqueous solution of acrylamide that concentration expressed in percentage by weight is 5~10% NIPAAm and 0.025~0.05%, carry out surface grafting polymerization 20~24 hours;
The polymerization perforated membrane that B) will carry out surface grafting is immersed in the isocyanate-terminated poly glycol monomethyl ether (being called for short NCO-MPEG); Reacted 15~20 hours down at 80~90 ℃; On the PNIPAAm of porous film surface grafted chain, connect hydrophilic polyethylene glycol side chain, obtain surface self-cleaning polymer porous membrane.
Among the preparation method of the surface self-cleaning polymer porous membrane that the present invention is above-mentioned, its further technical scheme is the poly glycol monomethyl ether (being called for short MPEG) that described polyethylene glycol side chain is a molecular weight 500~4000.
Among the preparation method of the surface self-cleaning polymer porous membrane that the present invention is above-mentioned, its further technical scheme can also be that the method that the polymer porous film that produces free radical is caused on described surface is a method of plasma processing; Further technical scheme is that described method of plasma processing is following again: polymer porous film is inserted in the plasma reaction chamber; At pressure is under the Ar atmosphere of 5Pa; With plasma treatment power 1~5W, the condition in 20~30 minutes processing times, cause the generation free radical on the polymer porous film surface.
Among the preparation method of the surface self-cleaning polymer porous membrane that the present invention is above-mentioned; The preparation method that its further technical scheme can also be described NCO-MPEG is following: MPEG is added drop-wise in the equimolar toluene di-isocyanate(TDI); Reaction is 6~10 hours in the presence of 60~70 ℃ of catalyst, obtains NCO-MPEG; Further technical scheme is that described catalyst is preferably stannous octoate, dibutyltin dilaurate or cobalt naphthenate again.
Among the preparation method of the surface self-cleaning polymer porous membrane that the present invention is above-mentioned, its further technical scheme can also be that described polymer porous film is polyvinylidene fluoride porous film, polypropylene porous film or polyethylene porous membrane.
Among the preparation method of the surface self-cleaning polymer porous membrane that the present invention is above-mentioned, the type that its further technical scheme can also be described polymer porous film is flat sheet membrane, hollow-fibre membrane or tubular membrane.
The present invention has following beneficial effect:
The present invention has connected hydrophilic polyethylene glycol side chain on the PNIPAAm grafted chain on modified porous film surface, overcome the adverse effect of the surface hydrophobic of the above PNIPAAm of LCST, and that has further improved the PNIPAAm grafted is difficult for contaminative and self-cleaning property.The surface grafting technology that adopts has given modified porous film surface lasting self-cleaning performance.Clean carrying out alternating temperature near the water of modified porous film temperature LCST, can reach surperficial self-cleaning purpose.Its automatically cleaning technology has simply, the characteristics of environmental protection.Because cleaning temperature is not high, can not damage polymer porous film.
The specific embodiment
Below through embodiment the present invention is done further explanation, the pollution experiment of perforated membrane and cleaning experiment method are following among the embodiment:
The pollution of perforated membrane experiment: be that 500ppm, pH value are that 5.0 bovine serum albumin(BSA) (BSA) aqueous solution is as pollution medium with concentration; In operating pressure 0.01MPa, temperature is under 40 ℃ of conditions simulating pollution to be carried out on the polymer porous film surface, until the water flux balance." water flux conservation rate " after the pollution=(polluting back water flux/initial water flux) * 100%
The cleaning experiment of perforated membrane: with deionized water as cleansing medium; (PNIPAAm) under near 40 ℃ the grafted chain lower critical solution temperature (LCST) and 30 ℃ of temperature the polymer porous film surface is cleaned gathering (N-NIPA) respectively; Operating pressure 0.01MPa; Until the water flux balance, " the water flux recovery rate " after the cleaning=(cleaning back water flux/initial water flux) * 100%.
Embodiment 1
The grafting on polymer porous film surface: polymer porous film is inserted in the plasma reaction chamber; At pressure is under the Ar atmosphere of 5Pa; With plasma treatment power 1W, the condition in 20 minutes processing times, cause the generation free radical on the polymer porous film surface.Under Ar atmosphere; The polymer porous film that above-mentioned surface is produced free radical immerse that to contain concentration expressed in percentage by weight be 5% N-NIPA (NIPAAm) with the aqueous solution of 0.025% acrylamide in polymerization 24 hours, prepare the polymer porous film of PNIPAAm surface grafting.
The hydrophilic modification of PNIPAAm grafted chain: poly glycol monomethyl ether (MPEG) is added drop-wise in the equimolar toluene di-isocyanate(TDI), and 70 ℃ were reacted 6 hours under the catalysis of stannous octoate, obtained isocyanate-terminated poly glycol monomethyl ether (NCO-MPEG).PNIPAAm polymers grafted perforated membrane and NCO-MPEG were reacted 15 hours down at 80 ℃; On the PNIPAAm grafted chain, connect hydrophilic MPEG side chain; Obtain surface self-cleaning polymer porous membrane, see attached list through pollution experiment and its performance of cleaning experiment of perforated membrane.
Embodiment 2
The grafting on polymer porous film surface: polymer porous film is inserted in the plasma reaction chamber; At pressure is under the Ar atmosphere of 5Pa; With plasma treatment power 1W, the condition in 30 minutes processing times, cause the generation free radical on the polymer porous film surface.Under Ar atmosphere; The polymer porous film that above-mentioned surface is produced free radical immerse that to contain concentration expressed in percentage by weight be 10% N-NIPA (NIPAAm) with the aqueous solution of 0.05% acrylamide in polymerization 20 hours, prepare the polymer porous film of PNIPAAm surface grafting.
The hydrophilic modification of PNIPAAm grafted chain: poly glycol monomethyl ether (MPEG) is added drop-wise in the equimolar toluene di-isocyanate(TDI); 60 ℃ were reacted 10 hours under the catalysis of dibutyltin dilaurate, obtained isocyanate-terminated poly glycol monomethyl ether (NCO-MPEG).PNIPAAm polymers grafted perforated membrane and NCO-MPEG were reacted 20 hours down at 80 ℃; On the PNIPAAm grafted chain, connect hydrophilic MPEG side chain; Obtain surface self-cleaning polymer porous membrane, see attached list through pollution experiment and its performance of cleaning experiment of perforated membrane.
Embodiment 3
The grafting on polymer porous film surface: polymer porous film is inserted in the plasma reaction chamber; At pressure is under the Ar atmosphere of 5Pa; With plasma treatment power 1W, the condition in 20 minutes processing times, cause the generation free radical on the polymer porous film surface.Under Ar atmosphere; The polymer porous film that above-mentioned surface is produced free radical immerse that to contain concentration expressed in percentage by weight be 8% N-NIPA (NIPAAm) with the aqueous solution of 0.035% acrylamide in polymerization 24 hours, prepare the polymer porous film of PNIPAAm surface grafting.
The hydrophilic modification of PNIPAAm grafted chain: poly glycol monomethyl ether (MPEG) is added drop-wise in the equimolar toluene di-isocyanate(TDI), and 70 ℃ were reacted 6 hours under the catalysis of stannous octoate, obtained isocyanate-terminated poly glycol monomethyl ether (NCO-MPEG).PNIPAAm polymers grafted perforated membrane and NCO-MPEG were reacted 15 hours down at 90 ℃; On the PNIPAAm grafted chain, connect hydrophilic MPEG side chain; Obtain surface self-cleaning polymer porous membrane, see attached list through pollution experiment and its performance of cleaning experiment of perforated membrane.
Embodiment 2-3 polymer porous film and surface modification condition see attached list 1, and polymer porous film and surface modification condition see attached list 1,2,3 among the embodiment 4-9 and in the relevant Comparative Examples, and other condition and method are with embodiment 1.
Table 1: the stain resistance of modified polyvinilidene fluoride perforated membrane and alternating temperature cleaning performance
Embodiment |
Polymer porous film and surface modification condition |
Initial water flux (L/m
2·h)
|
Pollute back water flux (L/m
2·h)
|
Water flux conservation rate (%) |
Clean back water flux (L/m
2·h)
|
Water flux recovery rate (%) |
Embodiment 1 |
Polyvinylidene fluoride porous film; The PNIPAAm surface grafting; The MPEG of molecular weight 500 modifies |
167.8 |
153.4 |
?91.4 |
166.5 |
99.2 |
Embodiment 2 |
Polyvinylidene fluoride porous film; The PNIPAAm surface grafting; The MPEG of molecular weight 1000 modifies |
165.4 |
156.3 |
?94.5 |
165.4 |
100.0 |
Embodiment 3 |
Polyvinylidene fluoride porous film; The PNIPAAm surface grafting; The MPEG of molecular weight 4000 modifies |
150.3 |
138.3 |
?92.0 |
150.0 |
99.8 |
Comparative Examples 1 |
Polyvinylidene fluoride porous film |
148.3 |
92.5 |
?62.4 |
116.3 |
78.4 |
Comparative Examples 2 |
Polyvinylidene fluoride porous film; The PNIPAAm surface grafting |
165.2 |
112.5 |
?68.1 |
161.9 |
98.0 |
Table 2: the stain resistance of modified polypropene perforated membrane and alternating temperature cleaning performance
Embodiment |
Polymer porous film and surface modification condition |
Initial water flux (L/m
2·h)
|
Pollute back water flux (L/m
2·h)
|
Water flux conservation rate (%) |
Clean back water flux (L/m
2·h)
|
Water flux recovery rate (%) |
Embodiment 4 |
Polypropylene porous film; The PNIPAAm surface grafting; The MPEG of molecular weight 500 modifies |
28.1 |
24.9 |
88.6 |
27.8 |
99.0 |
Embodiment 5 |
Polypropylene porous film; The PNIPAAm surface grafting; The MPEG of molecular weight 1000 modifies |
27.5 |
25.2 |
91.5 |
27.3 |
99.2 |
Embodiment 6 |
Polypropylene porous film; The PNIPAAm surface grafting; The MPEG of molecular weight 3000 modifies |
24.1 |
21.8 |
90.4 |
24.0 |
99.4 |
Comparative Examples 3 |
Polypropylene porous film |
25.3 |
13.1 |
51.8 |
17.4 |
68.6 |
Comparative Examples 4 |
Polypropylene porous film; The PNIPAAm surface grafting |
27.8 |
17.3 |
62.1 |
26.5 |
95.4 |
Table 3: the stain resistance of modified poly ethylene perforated membrane and alternating temperature cleaning performance
Embodiment |
Polymer porous film and surface modification condition |
Initial water flux (L/m
2·h)
|
Pollute back water flux (L/m
2·h)
|
Water flux conservation rate (%) |
Clean back water flux (L/m
2·h)
|
Water flux recovery rate (%) |
Embodiment 7 |
Polyethylene porous membrane; The PNIPAAm surface grafting; The MPEG of molecular weight 500 modifies |
95.6 |
85.7 |
89.6 |
95.2 |
99.6 |
Embodiment 8 |
Polyethylene porous membrane; The PNIPAAm surface grafting; The MPEG of molecular weight 2000 modifies |
92.5 |
83.6 |
90.4 |
91.9 |
99.4 |
Embodiment 9 |
Polyethylene porous membrane; The PNIPAAm surface grafting; The MPEG of molecular weight 4000 modifies |
88.7 |
81.2 |
91.5 |
88.7 |
100.0 |
Comparative Examples 5 |
Polyethylene porous membrane |
90.4 |
52.7 |
58.3 |
64.7 |
71.6 |
Comparative Examples 6 |
Polyethylene porous membrane; The PNIPAAm surface grafting |
95.2 |
62.5 |
65.7 |
92.5 |
97.2 |
Water flux in the subordinate list is data under 40 ℃ of conditions, can find out from above result, and the polymer porous film surface of long time without surface modification is subject to the pollution of protein, causes water flux to descend significantly, and after water temperature changing cleaned, the recovery rate of water flux was not high yet; Behind the PNIPAAm surface graft modification, the anti-protein contamination performance on polymer porous film surface has certain improvement, and after water temperature changing cleaned, the water flux recovery rate reached 95%~98%; Through the PNIPAAm surface graft modification and after connecting hydrophilic MPEG side chain on the PNIPAAm grafted chain; Overcome the easy contaminative that the surface hydrophobic of the above PNIPAAm grafted chain of LCST causes; The anti-protein contamination performance on polymer porous film surface is significantly improved; After water temperature changing cleaned, the water flux recovery rate was near 100% simultaneously.