To achieve uniform electrospun PCL nanofibers, consider using a chloroform-ethanol solvent system and optimizing voltage, distance, and feed rate. Adjusting environmental conditions like humidity and temperature can also help prevent bead formation and achieve fibers within the 200–300 nm size range.

You can try acetic acid 90% aqueous solution to dissolve PCL overnigtht and up to 10% concnetration easily.This solution can be electrospun.

Your experimentation examined high polymer solutions containing 13–14 wt % PCL in chloroform/DMF without adjusting essential parameters like solution viscosity and solvent volatility and electrospinning settings and environmental factors and finish treatment procedures. The study omitted testing alternative solvent combinations such as THF or HFIP along with surface tension modulation additives even though these methods remain necessary to prevent bead formation in producing PCL nanofiber diameters under 300 nm. The production of bead-free and smooth PCL nanofibers with dimensions between 200 and 300 nm depends on both process parameter and solution parameter optimization. A PCL solution composed of 8–12 wt % would be ideal instead of 13–14 wt % because high polymer content creates thick solutions that lead to bead formation during electrospinning.

But you may do as follows:

Combining tetrahydrofuran (THF) for finest fibers or chloroform/DMF with ratios between 70:30 to 80:20 v/v enables proper solvent volatility alongside jet stability.

PMC

Including small quantities of a high-weight molecular chain carrier, such as polyethylene oxide (PEO with 10 weight percent), produces improved chain entanglement, which leads to bead suppression.

MDPI

Surface tension lowering occurs using small ethanol co-solvent amounts and trace amounts of Triton X-100 surfactant to produce continuous jet formation without bead formation

De Gruyter B, The optimal electrospinning parameters require setting an applied voltage between 15 to 20 kV together with a flow rate of 0.5 to 1 mL per hour and using a tip-to-collector distance between 12 to 16 cm for proper jet stretching and solvent evaporation.

Twenty-five degrees Celsius to twenty-five degrees Celsius with thirty percent to fifty percent relative humidity will stabilize the whipping jet system while preventing defects.

The last step involves two procedures which include vacuum drying at 40 °C for 12 h followed by optional thermal annealing at 40–60 °C to remove solvents and enhance fiber crystallinity and mechanical strength.

The dissolving of PCL using hexafluoroisopropanol (HFIP) solution provides bead-free PCL fibers at lower concentrations yet requires efficient cost and volatility management.