Morphology evolution of droplets in a polymer based extensional flow

Abstract

Fused Deposition Modelling (FDM) is one of the most widely used Additive Manufacturing (AM) methods to bring products to life. This thesis examines the incorporation of liquid additives into the nozzle region of an FDM system and attempts to understand their behavior in the polymer melt flow. The current computational work provides a background for a novel method wherein liquid additives can be injected into the melted polymer. A converging nozzle providing a near constant extension rate along the center-line is modelled. The deformation of droplets inside a polymer undergoing a purely extensional flow is studied for a range of exit (V) to platen velocities (U) and viscosity ratios (λ). It is observed that the behavior of droplets for a λ = 1 is found to be drastically different from that of lower λ's, which is attributed to the balance of shear stresses at the interface of the inner and outer flow fields. Finally, the morphology of the deposited plastic strands is also predicted. It is seen that as the velocity ratio (V/U) is increased the cross-section of the deposited strand changes from being almost spherical to an oblong.