Porous electrospun polycaprolactone (PCL) fibres by phase separation

The effect of different binary solvent systems on the size and surface morphology of electrospun poly(ε-caprolactone) (PCL) fibres was investigated in this study. Chloroform (CF), dichloromethane (DCM), tetrahydrofuran (THF) and formic acid (FA) were used in mixtures with dimethyl sulfoxide (DMSO) in order to generate pores on the fibre surface, through a non-solvent induced phase separation mechanism. The production of porous, bead free fibres with an average diameter ranging from 1470 to 2270 nm was achieved using 12.5% w/v PCL in CF/DMSO solution with good/poor solvent ratios varying from 75-90% v/v at the applied voltage of 15 kV, a spinning distance of 20 cm, and the feed flow rate of 1 ml/h. DCM and THF were proven to be less suitable good solvents for the process due to the formation of a solid skin on the jet surface, caused by the limited diffusivity of the polymer molecules from the jet surface to the liquid core and its subsequent collapse. FA was found to be unsuitable due to its similar evaporation rate to DMSO. The pore formation was favoured at high good/poor solvent ratios, whereas, the production of fibres with ribbon cross sections or fibres with beads was more pronounced at low good/poor solvent ratios. Data fitting was used for the development of a second order polynomial equation, correlating the produced fibre average diameter to the solution parameters (conductivity, surface tension, and viscosity), for the given polymer and solvent systems, under the specific experimental conditions used in this study. The ternary mixture compositions that lead to the formation of porous fibres were mapped on a ternary graph.