Dear Somashekara,

How are you storing the HF membranes? Are you storing it in distilled water or tap water? As PSF is hydrophobic polymer, storing HF membranes in normal tap water may cause fouling or ageing to membrane. Thus the performance can be affected. Being hydrophobic in nature PSF membranes are susceptible to organic foulant (bacteria or other microbes). Now, to mitigate this problem you can store your membrane in distilled water after adding few drops of formalene  within the water. I hope this will be helpful!

Best wishes

Munmun

Dear Munmun Mukherjee,

Thanks a lot for the answer.

The fiber bundles are stored at room temperature. PVP induces hydrophilic nature and so I guess it is not highly susceptible for fouling and cant be aged that fast, as such the performance parameters drops in 2 weeks of time. Correct me if I am wrong.

Kind regards,

Koushik

Dear Koushik Ayalasomayajula 

You are absolutely correct. Just being a little curious to know whether you noticed any change in morphology (surface roughness, pore size, contact angle) after the storage of HF membranes.

Regards

Munmun

Dear Munmun Mukherjee,

I am planning to perform SEM (on top and cross sectional surfaces) , AFM and still searching for suitable method to find out contact angle for porous HF membrane.

Could you give any idea on how to find out the pore size without involving contact angle. I was going through porometry (LLDP) and it requires contact angle as input data.  

Dear Koushik Ayalasomayajula,

You can go for BET (Brunauer–Emmett–Teller) analysis to measure the pore size as well pore distribution. In our lab we follow this method.

Dear Munmun Mukherjee,

Thanks a lot. I will look at that method.

Based on your description, it would be surprising if bacterial contamination was not a main cause for performance decline - see how commercial membrane samples are stored to prevent this.  If you did not do a thorough job of washing out the DMAc, you may be getting slow aging as well - not usually a problem with commercial samples.

Dear Sudhir Kulkarni,

Thanks a lot for the response.

DMAc is washed out from the fiber properly. At least the amount of DMAc left over is not the main cause for such a decrease, is what we observed. Could there be any reason other than bacterial contamination and DMAc for such drop?

Kind Regards,

Koushik

Unless you are spinning with very open morphology that may slowly densify, well stored Psf fiber should theoretically give you stable readings in clean water readings.  I remember one report (Fane) where cleanliness of the DI water was not sufficient for stable water measurements, they had to add an additional pre-filtration step to the test water.  Basically, water flux is so high that small problems (particulates, bacteria, bacterial remnants)  can become measurable.

Leaching of PVP over time.