Field-Assisted Crystallization of Thermoplastic Polyurethane During Continuous Processing: A Falsifiable Thermodynamic–Kinetic Framework for Electric, Magnetic, and Hybrid Fields

Abstract

This work develops a falsifiable thermodynamic–kinetic framework to investigate whether external electric fields, magnetic fields, or their combination can modify crystallization in thermoplastic polyurethane (TPU) during continuous processing.The framework distinguishes crystalline order from orientational order and couples them through a symmetry-consistent Landau-type free-energy formulation. Electric and magnetic fields are introduced through dielectric and magnetic-susceptibility anisotropies, while a higher-order electric–magnetic interaction term is retained as an experimentally identifiable parameter. Positive synergy, additive behavior, and antagonistic interaction are therefore all admissible outcomes.The thermodynamic description is coupled to nonequilibrium processing through temperature history, cooling rate, residence time, flow-induced orientation, orientational relaxation, and nucleation–growth kinetics. The resulting framework is intended to describe continuous processing routes such as corotating twin-screw extrusion followed by pelletization.The engineering objective is formulated as a target-matching problem in which the crystallinity obtained during twin-screw processing under an applied field is compared with an experimentally determined reference crystallinity from a belt-line process. No numerical reference crystallinity is assumed.The framework is intentionally formulation-independent at the conceptual level and may be applied to different TPU chemistries, including polyester-, polyether-, polycaprolactone-, and polycarbonate-based systems, provided that the relevant thermodynamic, dielectric, magnetic, and kinetic parameters are experimentally identified for the specific material.The manuscript defines dimensionless feasibility criteria, a parameter-identification strategy, electric-only, magnetic-only, and hybrid-field hypotheses, and an experimental falsification plan. The work does not assume that external fields necessarily enhance crystallization; rather, it establishes the conditions under which such an effect could be measured and potentially exploited within the finite residence time of an industrial process.This document is presented as a theoretical framework and preprint. Its predictions require experimental validation using the target TPU formulation and the actual thermal and residence-time history of the intended continuous-processing route.