I am preparing PVDF membranes with DMAc. PVDF was dissolved in DMAc to get 15% w/w solution. The dissolution was done at 45 C for 24 h. After dissolving, the solution was kept without stirring for 24 h for the removal of air bubbles. When I spread the solution on a glass plate using a 250-micrometer blade height, I found empty patches on the plate that increase in size with time.
I thought of the impurity and tried different solutions. I dried the PVDF completely at 60 C before use. I have used 3 different sources of PVDF. I have varied the mixing temperature. But all the time I was finding this issue.
Did anyone also found this problem? In the figure, you can see the patches, I am talking about.
I think PVDF polymer is hard to be casted as free standing. Also, viscosity of the prepared solution may be so low to be casted. The speed of casting too. I advice to cast over non-woven.
i used to prepare the same way before. There was not any issue before. but now I do not know the issue. As of the concentration of polymer, it is ok. The concentration was 15%, however, there are numerous articles with 12% polymer.
Dear Hassan,
I used PVDF/DMAc for preparing many UF membranes. This phenomenon is because of the low viscosity. I think you are using Kynar PVDF. Kynar class of PVDF creates lower viscosity in comparison with Solef grade. Actually in the same polymer concentration, the higher the molecular weight of the polymer, the higher the viscosity of the polymeric solution would be. You have to use the same grade if you wanna use the information of a reference. You have two choices: Use higher PVDF concentration Or use another grade of PVDF with higher molecular weight. Using non-woven polyester as a support cannot help you to solve this issue. I used 14wt% PVDF prepared by polyester support and saw these defects. The best viscosity was around 17-18wt% polymer for me with Solef1015 (Mw=573000).
Regards
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