Modeling of downstream heating in melt electrospinning of polymers

Abstract

In this study, both modeling and experimental approaches are used to demonstrate that downstream volumetric heating of electrospun fibers during melt electrospinning can result in markedly decreased fiber diameters. Previous melt electrospinning techniques were limited to production of micron‐sized fibers. This is because high viscosity and low electrical conductivity of the polymer melt coupled with rapid heat loss to the surroundings resulted in solidification of the jet before it had been significantly stretched by the electric field. In our study, we utilize a model for non‐isothermal melt electrospinning in the presence of a volumetric heat source. Our simulation results demonstrate that downstream heating does reduce the fiber diameter, and is therefore a feasible approach for resolving the limitations of melt electrospinning. In addition, our model has also been used to capture the effect of the surrounding temperature, which affects the thinning of the fiber through surface rather than volumetric interactions. Finally, melt electrospinning experiments are utilized to validate the model predictions for downstream heating. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1393–1405

Wire Melt Electrospinning of Thin Polymeric Fibers via Strong Electrostatic Field Gradients

“…This often confines the thinning of the jet to a region in the vicinity of the Taylor cone where the jet is still in the melted state. Since the heat loss occurs on the surface of the jet (interface of the jet with air), the heat loss to the environment increases as additional thinning occurs due to the increased surface area to volume ratio of the jet …”

“…However, as the rate of heat loss from the polymer jet to the surrounding environment is proportional to the surface to volume ratio of the polymer (i.e., inversely proportional to the jet diameter), smaller diameters require higher input power. As the diameter of the jet is reduced to a few microns, the input heat required to counter the heat loss effectively becomes excessively large . Moreover, the addition of nanoparticles may limit the applications of the processed fibers due to undesired changes in properties of the polymer as well as increased viscosity …”

“…Given the unfavorable scaling of the pressures required to push a polymer melt through a needle with the needle diameter (governed by Hagen–Poiseuille law), the jet confinement will be effective only if successfully implemented without physical walls. This approach is partly motivated by prior studies which suggest a direct correlation between the initial jet diameter and the diameter of the melt electrospun fibers …”

“…Since the heat loss occurs on the surface of the jet (interface of the jet with air), the heat loss to the environment increases as additional thinning occurs due to the increased surface area to volume ratio of the jet. [34][35][36] Theoretically, one may use smaller needles to achieve small fibers via syringe melt electrospinning. However, reducing the needle diameter (R) is not an effective strategy, since it will drastically increase the pressure drop (ΔP) along the needle (ΔP ∝ R −4 ).…”

“…As the diameter of the jet is reduced to a few microns, the input heat required to counter the heat loss effectively becomes excessively large. [34] Moreover, the addition of nanoparticles may limit the applications of the processed fibers due to undesired changes in properties of the polymer as well as increased viscosity. [40] In light of the above opportunities and challenges, a remedy to reduce the diameter of melt electrospun fibers can be sought by lowering the initial diameter of the jet (i.e., the Taylor cone size), or simple geometrical confinement of the jet.…”