Chemical phase separation is a common method for producing membranes, especially for microfiltration, ultrafiltration and nanofiltration applications. The technique employs controlled layering of polymer solutions to create porous structures. There are three main methods of chemical phase separation:
Non-solvent-induced phase separation (NIPS):
In this method, a polymer solution is cast onto a support and immersed in a non-solvent bath, usually water. The non-solvent bath precipitates the polymer and forms a porous structure. The NIPS process can be divided into the following steps:
1. Preparation of casting solution: Dissolve the appropriate polymer in a solvent or solvent mixture to form a homogeneous solution.
2. Casting solution: The polymer solution is cast onto a support, usually a glass plate or a nonwoven backing, using a casting knife to control the thickness of the resulting film.
3. Immersion Precipitation: The casting solution is immediately immersed in a non-solvent bath, usually water. The exchange of solvent and non-solvent leads to phase separation and precipitation of the polymer.
4. Membrane washing and drying: After phase separation, the resulting membranes are thoroughly washed to remove residual solvents and non-solvents, and then dried under controlled conditions.
Suitable for producing membranes with good mechanical strength and a wide range of pore sizes, NIPS is a relatively simple and cost-effective process. is a proven method in the production of filtration membranes and can be easily scaled up for large-scale production.
Thermally Induced Phase Separation (TIPS):
TIPS involves the use of polymer solutions with temperature sensitive solvents. By changing the temperature, the solubility of the polymer changes, causing phase separation and the formation of a porous structure. The TIPS process includes the following steps:
1. Preparation of casting solution: Dissolve the appropriate polymer in a temperature-sensitive solvent or solvent mixture to form a homogeneous solution.
2. Casting solution: The polymer solution is poured onto the carrier, the same as the NIPS process.
3. Temperature-induced phase separation: Exposure of the casting solution to controlled temperature changes (heating or cooling) causes the polymer to precipitate and form a porous structure.
4. Membrane Washing and Drying: The resulting membrane is washed to remove residual solvent and then dried under controlled conditions.
Compared with NIPS, the production process of TIPS can produce membranes with more uniform pore size distribution, but due to the heating process, TIPS may require more energy consumption, which will undoubtedly increase production costs, so TIPS is not as common as NIPS, and scaling up the process may require more energy. Much research and development.
Vapor Phase Separation (VIPS):
In the VIPS method, phase separation is induced by exposing a cast polymer solution to a non-solvent vapor atmosphere. The steps involved in the VIPS process are:
1. Preparation of casting solution: Dissolve the appropriate polymer in a solvent or solvent mixture to form a homogeneous solution.
2. Casting solution: The polymer solution is poured onto the carrier, the same as the NIPS process.
3. Vapor-induced phase separation: The casting solution is exposed to a non-solvent vapor atmosphere, which leads to solvent evaporation and non-solvent absorption, resulting in phase separation and precipitation of the polymer.
4. Membrane washing and drying: The resulting membrane is washed to remove residual solvents and non-solvents, and then dried under controlled conditions.
Gas phase separation can produce membranes with very uniform pore structure and size distribution, but this method may require specialized equipment and a controlled environment, which also increases production costs. Gas phase separation is less commonly used than NIPS and requires more research and development before it can be produced on a large scale.
All three processes above can be further optimized and customized to control the morphology and properties of the resulting membranes by adjusting variables such as polymer concentration, casting solution temperature, non-solvent type, and processing conditions. The choice between NIPS, TIPS and gas phase separation depends on the required membrane properties, production cost and scalability, conduct a thorough analysis of these factors and consult the technical team to determine the best method for your specific application. Additionally, it is imperative to stay abreast of the latest research and industry trends to ensure the best decisions are made for your product.
Citation
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2. Huang, R. Y. M.,& Rempel, G. L. (1995). Formation of microporous membranes by thermallyinduced phase inversion. Journal of Applied Polymer Science, 56(11), 1421-1432.https://doi.org/10.1002/app.1995.070561105
3. Reis, R. P., &da Costa, C. A. (2004). Chemical and physical characterization of polyamidereverse osmosis membranes formed by interfacial polymerization. Journal ofMembrane Science, 245(1-2), 53-64. https://doi.org/10.1016/j.memsci.2004.07.009
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