Yes different environmental conditions can cause such changes in fiber morphology. Though for PLA, your results are rather extreme; what is your solvent? I would recommend to record the rel. humidity and see for the stable "window". Alternatively, increase the concentration might also help to stabilize the process for the moment.

You have to compare the lab environment, such as humidity and temperature.

The possibility of changing viscosity varies with laboratory temperature

Thank you for all contributions. The equipment is in the closed chamber and i can arrange the temperature, but i can not adjust the humidity. As you can see at the attachment, I have three different type of fibers (beaded, spindle-like and smooth) with the same solution concentration and process parameters. Is it possible that the environmental conditions affect the fiber type so much?

Dear Yelda,

By looking at your PLA nanofibers of uniform diameter (smooth aspect) I will say that your results are quite optimistic!

Regarding the last experiments where the nanofibers are less uniform, you have received some possible explanations given by other RG colleagues.

What can be the source of these problems? I will recommend taking in consideration some factors which can, more or less, influence PLA spinning process: modification of viscosity of PLA solution (i.e., increase of viscosity by loss of solvent(s), apparition of some gels, etc.), modification of electrical parameters/conductivity of PLA solution, do not totally exclude the electrospinning device/needles and the experimental setup, others?

On the other hand, I believe that could be helpfully some experience already shared on this subject in literature:

CASASOLA, R. et al, 2014. Electrospun poly lactic acid (PLA) fibres: effect of different solvent systems on fibre morphology and diameter. Polymer, 55 (18), pp. 4728 – 4737

https://www.sciencedirect.com/science/article/pii/S0032386114005266

Muhammad Ashfak Jahangir, et al.,, Poly Lactic Acid (PLA) Fibres: Different Solvent Systems and Their Effect on Fibre Morphology and Diameter, American Journal of Chemistry, Vol. 7 No. 6, 2017, pp. 177-186. doi: 10.5923/j.chemistry.20170706.01.

Good luck in your research work and best regards,

Marius

PS: For your consideration

https://www.researchgate.net/post/How_can_I_prepare_PLA_polylactic_acid_for_electrospinning

http://electrospintech.com/espinflowchart.html#.XDI9mVxA45t

It depends on the environmental temperature, humidity, needle diameter, solution viscosity, electrospinning machine setup and solution preparation procedure. There is always a variation between the datas you have to optimize the parameters a lil bit.

Yes different environmental conditions can cause such changes in fiber morphology. Though for PLA, your results are rather extreme; what is your solvent? I would recommend to record the rel. humidity and see for the stable "window". Alternatively, increase the concentration might also help to stabilize the process for the moment.

Did you synthesize the polymer in the laboratory or a commercial product? As you know, PLA is a biodegradable polymer. The polymer may have been degraded and therefore the molecular weight may have changed. Molecular weight is an important parameter for electrospinning studies. I recommend that you see if the polymer has been degraded and you check the storage conditions.