(639e) Entanglement Kinetics in the Discrete Slip-Link Model

Additive manufacturing processes such as fused filament-fabrication are inherently non-equilibrium and non-isothermal; polymer molecules are stretched and oriented as they flow through the nozzle, and the melt disentangles. The printed layers quickly cool at approximately 100 C/s, “freezing-in” the non-equilibrium state of the polymer. This degrades the mechanical performance of printed objects by reducing the number of entanglements between chains spanning interlayer welds. Development of predictive models for material properties of printed objects thus requires a detailed understanding of polymer disentanglement kinetics. We use the discrete slip-link model to model polymer disentanglement under flow. The sliding of the Kuhn segments of a molecule through entanglements are modeled as a continuous-time Markov process. Entanglements are modeled as two body interactions by enforcing an equality between the rates of disentanglement and re-entanglement at the chain ends and in the chain interior. We find the distribution entanglements along the chain is non-uniform following cessation of a steady shear flow; entanglements initially form at the chain ends before moving inwards via slow reptation. This behavior is a possible contributor to observed residual stresses that remain after the printed objects cool.