Process and control key points of thermally induced phase separation microporous membrane

Thermally induced phase separation (TIPS) is a widely used method for the production of microfiltration membranes. It involves the formation of a homogeneous mixture of polymer and diluent (usually a low molecular weight compound), followed by a controlled cooling process that causes the polymer and diluent to phase separate. Phase separation produces a porous structure that can be further solidified by cooling or solvent extraction to obtain the desired microporous membrane.

The detailed process conditions of TIPS include the following steps:

1.Polymer Selection: Select the appropriate polymer with desired properties such as chemical resistance, mechanical strength and filtration performance. Common polymers used in TIPS include polypropylene (PP), polytetrafluoroethylene (PTFE), polyethylene (PE), and polyvinylidene fluoride (PVDF).

2.Diluent selection: When selecting a diluent, the compatibility between the polymer and the diluent must be considered. You can choose a diluent that is compatible with the selected polymer and has a known melting point or boiling point, so that it can form a uniform diluent when heated. Common diluents include paraffin, naphthalene, and dibutyl phthalate.

Mixture Preparation: Prepare a homogeneous mixture of polymer and diluent by heating them together until they are completely dissolved, as proper mixing and heating are critical to achieve a homogeneous mixture and avoid defects in the final film, in practice In our actual production, the mixture is usually heated to a temperature above the melting point of the polymer and diluent.

3.Cooling process: The mixture is cooled to induce phase separation, thereby forming a porous structure. Cooling rate, temperature, and duration can significantly affect the pore size, morphology, and overall structure of the film, and controlling the cooling rate is critical to achieve the desired pore size and morphology. Slower cooling rates generally result in larger pore sizes, while faster cooling rates result in smaller pore sizes.

4.Curing: Once the desired porous structure is obtained, the membrane is cured by further cooling or solvent extraction to remove the diluent. In some cases, non-solvents can be added to facilitate the extraction process, and the correct choice of solidification method (cooling or solvent extraction) and conditions can guarantee the mechanical strength and filtration performance of the membrane.

5.Post-processing: In the actual application process, each customer has different requirements for the membrane. Therefore, the membrane needs to be post-treated to achieve the required effect. The measures taken include annealing or surface modification, etc. Additional processing to improve its characteristics or performance, to meet the standards required by the customer.

In summary, thermally induced phase separation is a versatile technique for producing microporous filtration membranes. Detailed process conditions and critical point control play a crucial role in determining the final characteristics and performance of the membrane.

Citation

1.Khulbe, K. C.,Matsuura, T., & Lamarche, G. (Eds.). (2015). Thermally Induced PhaseSeparation in Polymer Membrane Science and Technology. Elsevier.

2.Xu, L., &Ding, J. (2016). Thermally induced phase separation (TIPS) method forfabrication of porous polymer membranes: state of the art and future prospects.Journal of Membrane Science, 514, 596-614.

3.Wang, Y., &Chung, T. S. (2019). Thermally induced phase separation (TIPS) membranes forwater treatment: a review. Journal of Membrane Science, 583, 278-301.

4.Huang, Y., Zheng,X., Chen, Y., & Wang, J. (2019). Recent advances in thermally induced phaseseparation membranes for water treatment. Journal of Materials Chemistry A,7(26), 15731-15749.

5.Shin, D. S., Kim,T. H., Choi, W. J., & Park, H. B. (2020). Recent advances inthermally-induced phase separation (TIPS) for the preparation ofhigh-performance membranes. Journal of Industrial and Engineering Chemistry,82, 166-179.