Atypical rheology and spinning behavior of poly(vinyl alcohol) in a nonaqueous solvent

Abstract

Electrospinning poly(vinyl alcohol), which is an important water-soluble biopolymer, using an organic solvent, such as dimethyl sulfoxide (DMSO), is particularly important for applications such as the controlled release of drugs with poor solubility in water. Since the nature of the solvent can greatly influence the morphology of the nanofibers and hence their bio-applicability, the rheology and electrospinning behavior of PVA in DMSO were investigated and compared with those in water. The viscosity, storage modulus and elasticity were found to be higher for PVA solutions in DMSO than in water for the same concentration of PVA. However, the fiber diameter obtained from the PVA-DMSO system was significantly lower. Although a linear correlation between the fiber diameter and elasticity could be established for the two solvents, their slopes were different. In a further investigation, a single linear equation could be determined for the two systems to give the relationship between the diameter and the number of entanglements per chain, suggesting that elasticity arising from chain entanglements was the key factor governing the fiber diameter. Solutions of PVA in DMSO exhibit higher viscosities and relaxation times compared to solutions of PVA in water and are expected to show higher fiber diameters on electrospinning. Contradictorily, the fiber diameters of electrospun fibers of PVA-DMSO system are lower than that of PVA-water system. This atypical behaviour arises due to pseudostructure formation in DMSO, thereby resulting in an increase in the viscosity and relaxation time but a drop in entanglements resulting in lower fiber diameters. Therefore, a direct correlation between entanglements per chain and fiber diameter was deduced.