CN114437339A

CN114437339A - Preparation method and application of high-absorbance honeycomb polyamide membrane

Info

Publication number: CN114437339A
Application number: CN202011207844.5A
Authority: CN
Inventors: 陈英波; 徐蛟鹏
Original assignee: Tianjin Polytechnic University
Current assignee: Tianjin Polytechnic University
Priority date: 2020-11-03
Filing date: 2020-11-03
Publication date: 2022-05-06
Anticipated expiration: 2040-11-03
Also published as: CN114437339B

Abstract

The invention discloses a simple preparation method of a honeycomb polyamide 6 membrane, which is characterized in that the honeycomb polyamide 6 membrane with quick self-stretching performance is obtained through graft modification, mixing of a pore-making agent and a classical non-solvent induced phase separation process. The graphene oxide in the invention not only changes the structural morphology of the polyamide 6 film, but also is used as a photo-thermal conversion layer, and simultaneously, the existence of a large number of pore defects improves the heat insulation performance of the material. The solar evaporation system also greatly improves the efficiency of steam generation in a local heating mode; the cellular surface roughness results in a system with a light absorption of approximately 99.9%. The honeycomb polyamide 6 film applied to solar evaporation has the characteristics of low cost, high stability, strong acid and alkali corrosion resistance, obtains excellent performance in multiple scenes such as seawater desalination, sewage treatment and the like, and shows huge practical application value and excavation potential.

Description

Preparation method and application of high-absorbance honeycomb polyamide membrane

Technical Field

The invention relates to the field of new materials, in particular to preparation and application of a honeycomb polyamide membrane with high light absorption rate and high water delivery performance.

Background

The development of human society has greatly accelerated the global energy consumption, especially in the natural environment and the reserve of fresh water resources. Due to the shortage of various resource and energy sources, people begin to look at sustainable development and renewable technology and energy exploration, such as wind energy, nuclear energy, tidal energy, biomass energy, solar energy and the like; among them, solar energy is recognized as a green energy source having the greatest development value in response to global environmental pollution and water resource shortage in the 21 st century due to its huge energy storage and regeneration capacity and convenience in natural acquisition. Meanwhile, with the rapid development and application of solar technology, solar heat collectors, solar thermal power generation, large-scale solar concentration systems, solar evaporation and other solar-based widely applied technologies gradually show potential practical application values and development prospects in fields closely related to human life, such as seawater desalination, sewage treatment and the like.

Currently, with the introduction of solar evaporation concept, i.e., the requirement of improving the photothermal conversion efficiency and the water vapor generation rate through the construction of local heating sites, various photothermal materials, such as biomass carbon, plasma absorbers, carbon materials, and some multilayer composite materials, have been developed. Various modes and forms have been designed to achieve the improvement of light absorption and high efficiency of photothermal conversion, while also achieving good evaporation performance. However, due to the complexity of the practical application environment, the stability of the solar evaporation system is very important, and the most ideal result is to obtain a high-efficiency and stable solar evaporation system suitable for various complex environments through the simplest preparation process.

Polyamide 6 is widely used in various engineering plastics as a material with good mechanical stability and corrosion resistance, is easy to process and has stable performance. But the performance of polyamide plastics in practical application is seriously influenced by the moisture absorption performance of the polyamide plastics, so that the polyamide plastics are often regarded as a lack of performance. However, there is a strong demand for "membrane" materials with continuous water supply in solar evaporation systems, and the moisture absorption properties of polyamide 6 membranes just meet this property requirement. Meanwhile, the stable mechanical property of the polyamide 6 composite material also provides possibility for the successful application of the polyamide membrane in a complex environment. Therefore, the preparation method of the honeycomb-shaped polyamide 6 film material with high light absorption rate and high water delivery performance based on polyamide 6 modification is provided, the honeycomb-shaped polyamide 6 film is obtained through a classical non-solvent induced phase separation (NIPS) process, the process is simple and convenient, the cost is low, the acid and alkali resistance is high, the evaporation performance of the polyamide film in a solar evaporation experiment is greatly improved, meanwhile, an excellent performance effect is obtained in multi-scene applications such as seawater desalination, sewage treatment and the like, and a huge excavation potential is shown.

Disclosure of Invention

Aiming at the technical problems, the invention provides a preparation method of a honeycomb-shaped film material with high absorptivity and high water delivery performance based on polyamide 6 modification. The surface appearance and structure of the polyamide 6 film are regulated and controlled by adding the graphene oxide and the pore-making agent lithium chloride, so that a large number of local hot spots are successfully constructed on the surface of the film while the water supply capacity required by an evaporation system is improved, and the light absorption rate and the evaporation performance of the whole system are greatly improved.

Therefore, the technical scheme of the invention is as follows:

synthesis of polyamide 6(PA6) composite material: firstly, adding a polymer monomer into a four-neck flask by adopting a one-pot method, adding 0.1-2 wt% of a dried graft modified monomer, heating and melting, mechanically stirring to uniformly disperse the graft modified monomer, raising the temperature to 220 ℃, and reacting at a constant temperature for 2 hours; then heating to 260 ℃, reacting for 2-8 h at constant temperature, and stopping reaction; and (4) quickly pouring out the polymerization product from the reaction vessel, and cooling to obtain the composite material.

Preparing a casting solution: cutting the composite material into small pieces by using an inclined jaw, placing the small pieces into pure water for cooking, and drying the product in a vacuum oven until the weight is constant. Taking a proper amount of the raw materials, slicing the raw materials, melting the raw materials in an acid solution to prepare a 10-25 wt% of membrane casting solution, then adding 1-20 wt% of a pore-forming agent, magnetically stirring the mixture for 10 hours at normal temperature until the mixture is uniformly dispersed, and defoaming the mixture in vacuum for 60-120 min to obtain the membrane casting solution.

Preparing a coagulating bath: comprises three types of coagulating baths; the first coagulation bath is an air bath, the second coagulation bath is a mixed solution of deionized water and 0.05-1.0 wt% of ethanol, and the third coagulation bath is deionized water.

Preparation of polyamide 6 film: and uniformly pouring a proper amount of the film casting liquid on a film scraping machine, setting the film scraping speed to be 30-60 mm/s and the temperature to be 25-30 ℃, then scraping the film on the film scraping machine at a constant speed, immersing the film in a second coagulating bath after the air bath is stable for 5-30 seconds, solidifying and forming a film in a phase conversion process, taking out the film after 5-10 minutes, immersing and storing the film in a deionized water coagulating bath for later use, and cutting the film into films with proper sizes when in use.

Further, the polymer monomer in the step 1) is one of caprolactam and 6-aminocaproic acid, caprolactam, polyamide 6 and polyamide 66 or a mixture of the caprolactam and the polyamide in any proportion.

Further, in the step 1), the grafting modification monomer is Graphene Oxide (GO), reduced graphene oxide (rGO), Carbon Black (CB), Carbon Nanotube (CNT) and molybdenum disulfide (MuS)₂) Or a mixture of any proportion.

Further, the specific gravity of the grafting modified monomer in the step 1) is 0.1-2 wt%.

Further, the acid solution in the step 2) is one of formic acid, acetic acid, hydrochloric acid, sulfuric acid and nitric acid or a mixed solvent in any proportion.

Further, the concentration of the casting solution in the step 2) is 10-25 wt%.

Further, the pore-forming agent in the step 2) is lithium chloride (LiCl) or calcium chloride (CaCl)₂) Lithium perchlorate (LiClO)₄) One or a compound of polyvinyl pyridine, polyoxyethylene and polyvinyl alcohol.

Further, the specific gravity of the hole making agent in the step 2) is 1-20 wt%.

Further, the second coagulation bath in step 3) may be methanol (CH)₃OH), chloroform (CHCl)₃) Hydrogen peroxide (H)₂O₂) And hydrogen chloride (HCl) or mixed in any proportion.

Further, the film scraping speed in the step 4) is set to be 30-60 mm/s, and the temperature is 25-30 ℃.

Further, the phase inversion process time of the polyamide film in the second coagulation bath in the step 4) is 5-10 min.

Compared with the prior art, the method has the following advantages:

the invention carries out graft modification on the polyamide composite material, greatly improves the hydrophilicity of the polyamide membrane on the basis of keeping the water absorption of the material, obviously improves the porosity, and supplies the water evaporated on the surface of the polyamide membrane in time and continuously.

The pore-making agent in the invention improves the pore distribution and the surface morphology of the polyamide 6 film, the surface roughness is obviously increased, and the light absorption rate in the wavelength range of 200-2500nm is as high as 99.8%.

The invention has the advantages of low manufacturing cost, simple and convenient process, good film forming property, strong acid and alkali resistance, high removal rate of various dyes and salts up to 99.9 percent, and suitability for various complex environments.

Drawings

FIG. 1 is a scanning electron microscope image of the honeycomb polyamide 6 film obtained in example 1. The surface appearance (a) of the pure polyamide 6 film, the water contact surface appearance (b) of the honeycomb polyamide 6 film, the honeycomb surface appearance (c) and the pore appearance (d) of the section;

FIG. 2 is a scanning electron microscope photograph of the surface topography of the water contact side (a) and the honeycomb (b) of the honeycomb polyamide 6 film obtained in comparative example 1;

FIG. 3 is a scanning electron microscope photograph of the surface topography of the water contact side (a) and the honeycomb (b) of the honeycomb polyamide 6 film obtained in comparative example 2;

FIG. 4 is a true color confocal photograph of the honeycomb polyamide 6 film obtained in example 1;

FIG. 5 is an infrared spectrum of a honeycomb polyamide 6 film obtained in example 1;

FIG. 6 is an infrared photograph showing the temperature distribution of the honeycomb polyamide 6 film obtained in example 1 before and after 60min of light irradiation.

Detailed Description

The technical solution of the present invention is described in detail below with reference to examples.

Example 1

1) Synthesis of Polyamide 6 composite: firstly, adding 3g of caprolactam and 27g of 6-aminocaproic acid serving as reaction monomers into a four-neck flask by adopting a one-pot method, adding 0.5 wt% of dried graphene oxide, heating and melting, mechanically stirring to uniformly disperse the graphene oxide, and carrying out programmed heating to 220 ℃ for reacting at a constant temperature for 2 hours; then heating to 260 ℃, reacting for 8 hours at constant temperature, and stopping reaction; and (4) quickly pouring out the polymerization product from the reaction vessel, and cooling to obtain the composite material.

2) Preparing a casting solution: cutting the composite material into small pieces by using an inclined jaw, placing the small pieces into pure water for cooking, and drying a product in a vacuum oven to constant weight. Taking a proper amount of the raw materials, slicing the raw materials, melting the raw materials in formic acid solution to prepare 20 wt% of membrane casting solution, then adding 9 wt% of lithium chloride serving as a pore-forming agent, magnetically stirring the mixture for 10 hours at normal temperature until the mixture is uniformly dispersed, and defoaming the mixture in vacuum for 60 minutes to obtain the membrane casting solution.

3) Preparing a coagulating bath: comprises three types of coagulating baths; wherein, the first coagulation bath is an air bath, the second coagulation bath is a mixed solution of deionized water and ethanol with the weight percent of 1.0, and the third coagulation bath is deionized water.

Scraping polyamide 6 film: and uniformly pouring a proper amount of the film casting solution on a film scraping machine, setting the film scraping speed to be 50 mm/s and the temperature to be 25 ℃, then uniformly scraping the film on the film scraping machine, immersing the film in a second coagulating bath after the air bath is stabilized for 10 seconds, carrying out coagulation film formation in the phase inversion process, taking out the film after 10 minutes, immersing and storing the film in a deionized water coagulating bath for later use, and cutting the film into films with proper sizes when in use.

The Scanning Electron Microscope (SEM) morphology of the polyamide 6 membrane obtained in this example is shown in FIG. 1, and from FIG. 1b, it is evident that the surface pore distribution and the pore size increase on the water contact surface are observed, and the surface tends to be smoother. From fig. 1c and 1d, the surface topography of the honeycomb and the cross-sectional pore topography can be observed. It can be seen from the true color confocal photograph of fig. 4 that the roughness of the honeycomb surface is significantly increased, thereby increasing the number of refraction times of light so that the light absorption rate is enhanced. Meanwhile, from the infrared spectrum of FIG. 5, it can be observed that the polyamide film vibrates due to the expansion and contraction of the C-H bond peculiar to the PA6 segment at a wavelength of 2860cm^-1And 2930cm^-1A stronger new peak appears at each position; at 1640cm^-1In which a C-0 group of an amide bond appearsA characteristic absorption peak of the stretching vibration; at the same time, at 1536cm^-1New peaks of bending vibration of N-H bonds and stretching vibration of C-N bonds in the amide groups appeared, confirming the successful preparation of the honeycomb polyamide 6 membrane.

Under the conditions that the ambient temperature is about 25 ℃ and the relative humidity is 35-45%, the test calculates that the illumination power of the honeycomb polyamide 6 film is 1kw m respectively^-2、2kw m^-2Then, the water evaporation amount, evaporation rate, evaporation efficiency, and light absorption rate of the film were illuminated for 60min, and the results were obtained as follows:

comparative example 1

The preparation process was essentially the same as in example 1, except that: in the step 2), a pore-foaming agent lithium chloride is changed into polyvinyl alcohol.

The SEM morphologies of the honeycomb polyamide 6 membrane obtained in the comparative example are shown in fig. 2a and 2b, which respectively represent the water contact surface and the surface morphology of the honeycomb, and the difference in the pore distribution on the membrane surface and the change in the pore size can be clearly observed.

Under the conditions that the ambient temperature is about 25 ℃ and the relative humidity is 35-45%, the test calculates that the illumination power of the honeycomb polyamide 6 film is 1kw m respectively^-2、2kw m^-2Next, the water evaporation amount, evaporation rate, evaporation efficiency, and light absorption rate of the film after 60min of light irradiation, and infrared photographs of the temperature distribution before and after light irradiation are shown in fig. 6, and the following results were obtained:

it can be seen from comparison with the comparative example that, when the concentration of the pore agent is changed into polyvinyl alcohol, the evaporation capacity, the evaporation rate, the evaporation efficiency and the light absorption rate of the membrane are all obviously reduced, and the above tests show that the type of the pore-forming agent determines the pore distribution and the pore diameter of the membrane surface, thereby influencing the stable continuity of a water supply channel and a water supply system, and in addition, the light absorption rate is also influenced due to the change of the surface morphology. Therefore, the selection of the proper pore-forming agent type is important for the solar evaporation performance.

Comparative example 2

2) Preparing a casting solution: cutting the composite material into small pieces by using an inclined jaw, placing the small pieces into pure water for cooking, and drying a product in a vacuum oven to constant weight. Taking a proper amount of the raw materials, slicing the raw materials, dissolving the raw materials in formic acid solution to prepare a 20 wt% membrane casting solution, then adding 9 wt% of a pore-forming agent lithium chloride, magnetically stirring the mixture for 10 hours at normal temperature until the mixture is uniformly dispersed, and defoaming the mixture in vacuum for 60 minutes to obtain the membrane casting solution.

3) Preparing a coagulating bath: two types of coagulation baths are included; wherein the first coagulation bath is an air bath, and the second coagulation bath is deionized water.

The Scanning Electron Microscope (SEM) morphology of the flat sheet membrane obtained in this example is shown in fig. 3, and from fig. 3a, the pore distribution and pore size reduction on the surface of the water contact surface can be clearly observed. From fig. 3b, the non-uniformity of the surface honeycomb distribution and the morphology of the breakage can be observed.

Under the conditions of ambient temperature of about 25 ℃ and relative humidity of 35-45%Next, the test calculated the respective illumination power of the honeycomb polyamide 6 film at 1kw m^-2、2kw m^-2Next, the water evaporation amount, evaporation rate, evaporation efficiency, and light absorption rate of the film were irradiated for 60min, and the results were obtained

The following were used:

examples 2 to 6

The preparation process was essentially the same as in example 1, except that: varying the concentration of GO in step 2).

The following table shows specific embodiments of examples 2 to 5

Examples 7 to 10

The preparation process was essentially the same as in example 1, except that: changing the concentration of the pore-forming agent in the step 2).

The present invention has been described in more detail with reference to the attached drawings and tables, but the present invention is not limited by the above-mentioned manner, and various modifications can be made within the scope of the present invention as long as the method concept and technical scheme of the present invention are adopted.

Claims

1. A preparation method and application of a honeycomb polyamide 6 film with high absorptivity are characterized by comprising the following steps:

1) synthesis of Polyamide 6 composite: firstly, adding a polymer monomer into a four-neck flask by adopting a one-pot method, adding 0.1-2 wt% of a dried graft modification monomer, heating and melting, mechanically stirring to uniformly disperse the graft modification monomer, raising the temperature to 220 ℃ by a program, and reacting at constant temperature for 2 hours; then heating to 260 ℃, reacting for 2-8 h at constant temperature, and stopping reaction; and (4) quickly pouring out the polymerization product from the reaction vessel, and cooling to obtain the composite material.

2) Preparing a casting solution: the composite material is cut into small pieces by using an inclined jaw, the small pieces are placed in pure water for cooking, and a product is dried in a vacuum oven to constant weight. Taking a proper amount of the raw materials, slicing and dissolving in an acid solution to prepare a 10-25 wt% of membrane casting solution, then adding 1-20 wt% of pore-forming agent, magnetically stirring at normal temperature for 10 hours until the pore-forming agent is uniformly dispersed, and defoaming in vacuum for 60-120 min to obtain the membrane casting solution.

3) Preparing a coagulating bath: comprises three types of coagulating baths; the first coagulation bath is an air bath, the second coagulation bath is a mixed solution of deionized water and 0.05-1.0 wt% of ethanol, and the third coagulation bath is deionized water.

4) Preparation of polyamide 6 film: and uniformly pouring a proper amount of the film casting liquid on a film scraping machine, setting the film scraping speed to be 30-60 mm/s and the temperature to be 25-30 ℃, then scraping the film on the film scraping machine at a constant speed, immersing the film in a second coagulating bath after the air bath is stable for 5-30 seconds, solidifying and forming a film in a phase conversion process, taking out the film after 5-10 minutes, immersing and storing the film in a deionized water coagulating bath for later use, and cutting the film into films with proper sizes when in use.

2. The method for preparing a cellular polyamide 6 membrane and its use according to claim 1, characterized in that: in the step 1), the polymer monomer is one of caprolactam, 6-aminocaproic acid, caprolactam, polyamide 6 and polyamide 66 or a mixture of the caprolactam and the polyamide 66 in any proportion.

3. The method for preparing a cellular polyamide 6 membrane and its use according to claim 1, characterized in that: the grafting modified monomer in the step 1) is Graphene Oxide (GO), reduced graphene oxide (rGO), Carbon Black (CB), Carbon Nano Tube (CNT) and molybdenum disulfide (MuS)₂) One or any proportion of the above componentsA compound (I) is provided.

4. The method for preparing a cellular polyamide 6 membrane and its use according to claim 1, characterized in that: in the step 1), the specific gravity of the grafting modified monomer is 0.1-2 wt%.

5. The method for preparing a cellular polyamide 6 membrane and its use according to claim 1, characterized in that: the acid solution in the step 2) is one of formic acid, acetic acid, hydrochloric acid, sulfuric acid and nitric acid or a mixed solvent in any proportion.

6. The method for preparing a cellular polyamide 6 membrane and its use according to claim 1, characterized in that: the concentration of the casting solution in the step 2) is 10-25 wt%.

7. The method for preparing a cellular polyamide 6 membrane and its use according to claim 1, characterized in that: the pore-forming agent in the step 2) is lithium chloride (LiCl) or calcium chloride (CaCl)₂) Lithium perchlorate (LiClO)₁) One or a compound of polyvinyl pyridine, polyoxyethylene and polyvinyl alcohol.

8. The method for preparing a cellular polyamide 6 membrane and its use according to claim 1, characterized in that: the specific gravity of the hole making agent in the step 2) is 1-20 wt%.

9. The method for preparing a cellular polyamide 6 membrane and its use according to claim 1, characterized in that: the second coagulation bath in step 3) may also be methanol (CH)₃OH), chloroform (CHCl)₃) Hydrogen peroxide (H)₂O₂) And hydrogen chloride (HCl) or mixed in any proportion.

10. The method for preparing a cellular polyamide 6 membrane and its use according to claim 1, characterized in that: in the step 4), the film scraping speed is set to be 30-60 mm/s, and the temperature is 25-30 ℃.

11. The method for preparing a cellular polyamide 6 membrane and its use according to claim 1, characterized in that: in the step 4), the time of the phase inversion process of the polyamide film in the second coagulation bath is 5-10 min.