Electrospinning of poly(lactic acid): Theoretical approach for the solvent selection to produce defect-free electrospun nanofibres

In this study an integrated methodology is proposed for the selection of solvent systems to produce electrospinnable solutions that form defect-free poly (lactic acid) fibres with narrow diameter distributions. The solvent systems are chosen using a thermodynamic approach, combined with electrical and rheological property criteria. More specifically, the three step methodology includes 1) initial choice of solvent by solubility evaluation to meet thermodynamic criteria, 2) electrical properties i.e. conductivity and dielectric constant adjustment by using solvent mixtures to meet electrical property criteria, and 3) critical entanglement concentration (Ce) determination by viscosity measurements, supported by elastic and plastic moduli measurements, followed by concentration adjustment to meet rheological criteria. All three criteria need to be met to ensure defect-free nanofibre morphology. The methodology is demonstrated using poly (lactic acid) solutions that were characterised in terms of thermodynamic properties, conductivity, surface tension and viscosity measurements. These data were analysed and related to the nanofibre morphology and diameter as determined from scanning electron microscopy (SEM). Measurements of the elastic (G’) and the plastic (G’’) moduli of PLA solutions showed a sharp increase of G’ at the chain entanglement concentration.