i am developing a polymer membrane of polyaryletherketone using solution casting method.each time i got brittle and crispy membrane, whereas i want smooth flexible membrane. i added Polyethylene glycol PEG(of M.wt 100k-300k) from 10-25 wt% to reduce brittleness but still its brittle and crispy. The method of drying followed is as under.
- dissolved PEG in NMP first and then added polymer to it.
- dissolved further for 24 hrs
- then heated to 80C to dissolve polymer and plasticizer well.
- Kept in oven at 60C for 24 hrs and 80C for 2 hrs.
- finally i cast it tio petri dish.
i do not know where the problem is? either in drying method or solvent or plasticizer( i also used DMSO but result is still same). i will be thankful if someone could guide and help me in this regard.
Thanks Dr paresh
answers to your questions are as under:
1.-----Molecular Weight of Repeat unit g/ mol-1 is 300.3 (PEKK)
2. ------ratio = 20:5:75( polymer:PEG:NMP)
the problem is that i couldn't find its Mn number average molecular weight because it requires Size Exclusion Chromatography and i do not have this facility.
Dear sir where may be the problem?
There are 3 possibilities: 1) You have an oligomer (a polymer with low average molecular mass) as Dr. Samantaray pointed out. 2) Casting the membrane from solution was not done well so the polymer crumbled. (Applying heating, as you described, may have not been needed in the first place). 3) The polymer, itself, does not form a flexible membrane. This last possibility needs confirmation by consulting references.
Thanks Dr nizar .its brittle because i have sulfonated my polymer. but after casting in a proper solution it should be flexible. it seems that the i didn't follow the procedure for casting the membrane properly as you pointed out in #2. would you plz guide me the heating and drying procedure to get a good flexible membrane, because i couldn't get a proper procedure and conditions to apply for getting a flexible membrane.regards
Please try to skip the step (no. 4 : Kept in oven at 60C for 24 hrs and 80C for 2 hrs.). DMSO is better replaced by a more volatile solvent. Good casting requires complete dissolution and leaving the solvent to evaporate by itself without an outside help by (e.g. heating).
When a membrane forms, there is need to pull it carefully by using tweezers.
I found it easy, in the past, to form films from amorphous atactic PMMA but that was not possible with isotactic PMMA "which has crystallinity. The film looked like your brittle membrane & just crumbled.
If after repeating your experiment, you get the same result then that is it & this is accepted as a scientific finding. You may move then to another polymeric system.
Thank you DR Nizar for your valuable information. when i dissolve sulfonated polymer in NMP it is not soluble at room temperature. after 24 hrs stirring i heat it to 60C-80C then it dissolves. is it ok to heat it at this temperature to dissolve it?
i will try now PVDF also and will leave it in open atmosphere to dry it. regards
Usually a hot water bath is used to help in dissolving a polymer together with continuous shaking. What you did is right; polymers need time to dissolve (e.g. 24 hours) or to form true solution.
Just a safety note: Dry your polymer in open atmosphere in a well-ventilated hood.
Many years ago I did solution casting of sulfonated polystryrene to form large polymer membrane sheets (measuring 8" x 11"). I used DMF solvent as well as various surfactants, with heating to remove the solvent. I'm sure your polymer system is quite different from what I did, but a switch to DMF may help.
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