An alternative solvent system for the steady state electrospinning of polycaprolactone

Polycaprolactone (PCL) is a biocompatible aliphatic polyester with many possible applications in the medical field. PCL nanofibres, produced by electrospinning, could provide new characteristics that are of interest for these applications. Nanofibrous structures indeed show unique properties such as higher specific surface area, higher porosity and smaller pore size compared to microfibres. At present the most commonly used solvent for electrospinning PCL is chloroform, but this only leads to fibres in the microscale range. A key issue in electrospinning PCL is thus the ability to obtain bead-free fibres with diameters in the nanoscale range. To obtain these small diameter nanofibres of PCL various solvent systems were examined. The innovative solvent mixture formic acid/acetic acid was found to allow for nanofibres with a diameter ten times smaller than the one obtained by chloroform. Steady state conditions could be obtained which thus allow electrospinning in a stable and reproducible way. Moreover, GPC measurements on the PCL pellet and the produced nanofibrous structures showed that there was no degradation of PCL during the electrospinning process from the acid solution. Further it was noticed that the average fibre diameter decreased with decreasing polymer concentration. The solvent ratio was found to have a minor influence on the fibre diameter but showed a significant effect on the fibre diameter distribution with a decreasing standard deviation with increasing amount of formic acid. Also the humidity, an often overlooked yet important parameter, was noted to affect both diameter characteristics. Generally it can be concluded that the solvent system formic acid/acetic acid could fill the gap in electrospinning PCL since it is readily able to produce uniform fibres in the nanoscale range