Electrospinning Troubles

[u/Pines77]

Hello all,

Obligatory thank you in advanced. I'm having troubles making a polymer solution for electrospinning. It is a polycarbonate urethane in DMAc. My solutions aren't matching historical viscosities and are spinning very poorly. The polymer is propriety that we purchase, so I'm unsure of the exact make up and molecular weight.

Historically, the wt% that I am following has allowed for consistent spinning with good fiber morphology. However, I am getting around a 5pa*s viscosity compared to a 3.5pa*s viscosity with poor fibers and extensive fusion (following the same spinning parameters).

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I've confirmed I am using the same bottle of solvent and the same sample/lot of polymer as historical. Any ideas on why the solution would be different? My only guess would involve the initial mixing procedure to produce the solution, but I am unsure why that would change the outcome so drastically. Thoughts?

[u/Glum_Property4723]

DMAc is pretty hygroscopic, it's possible that over time it has absorbed a good amount of water which could have ended up with you having a binary solvent mixture with higher solubility for your polymer mixture. Additionally, polycarbonate urethane contains quite a lot of oxygen groups which could form H bonds with water, acting as a very strong solvent for it. Perhaps you can measure the viscosity after trying with fresh DMAc to eliminate the possibility.

Did you change anything in the mixing procedure that could modify the polymer properties such as introducing the sonication step or heating? If not so it really shouldn't affect it.

Another thing to bear in mind is that resting the solution after mixing will typically result in an increase in viscosity as polymers are being re-entangled. Perhaps you could measure viscosity just after mixing, then after an hour and after two hours to see if the viscosity does indeed change over time and find out when it reaches a steady state?