“In‐situ” monitoring of the non‐isothermal crystallization of polymers by dielectric spectroscopy

Abstract

AbstractIn recent years, experimental techniques based on microdielectrometry have attracted increasing interest for continuous monitoring, in a nondestructive way, of the advancement of the reaction of thermoset resins under cure. The extension of this technique for “in‐situ” monitoring of the crystallization of thermoplastics has been carried out. A correlation between the evolution of the dielectric parameters of the material and its viscoelastic properties was done. A dynamic rheometer equipped with a dielectric cell and an instrumented slit die was designed. The crystallization process is depicted by a conductivity drop and by the occurrence of a maximum in the real permittivity. The decrease of the specific conductivity results from a modification of the conductive paths, whereas the increase of the permittivity is due to an interfacial polarization phenomenon (so‐called Maxwell Wagner Sillars effect) between the amorphous phase and the growing crystalline entities. The sudden variation of the dielectric response is envisioned as a means for following the progression of the crystallization front within a mold. The description of the crystallization with Nakamura's model allowed the modeling of the crystallization inside a mold. The evolution of the temperature profile and of the crystallinity rate is modeled by a classical finite difference method. Dielectric measurements performed at controlled cooling rate experiments are in good agreement with the numerical simulation results and confirm the usefulness of dielectric measurements for “In‐situ” monitoring of the crystallization process of a polymer inside a mold.