Rheological aspects in fabricating pullulan fibers by electro-wet-spinning

Electro-wet-spinning was used to fabricate continuous nonwoven microscale and nanoscale fibers from pullulan. We investigated the rheological properties of pullulan dispersions using DMSO:water mixtures as solvents with varying compositions. The relationship between electrospinnability and rheological properties were studied. In order to obtain well-formed pullulan fibers, the concentration of pullulan dispersion had to be 1.88-2.25 times the entanglement concentration, depending on DMSO:water ratio in the solvent. Shear viscosity was another important factor. The shear viscosities at 100s^-1 of electrospinnable pullulan dispersions fell into a range between 0.06 and 2.2Pas, regardless of solvent composition. Yet, there may still be other factors governing the fiber size as DMSO concentration changed. Pullulan fibers in the order of hundreds of nanometers to tens of microns were obtained. Increase in DMSO concentration in the solvent generally increased the fiber size and pore size in the electrospun pullulan fiber mat.