CRYSTALLIZATION STUDIES OF SEMI-CRYSTALLINE POLYMERS UNDER OSCILLATORY SHEAR USING THE RHEOMETRICS MECHANICAL SPECTROMETER

A method has been developed on the Rheometrics mechanical spectrometer using the eccentric rotating disks mode to study the crystallization kinetics of different semi‐crystalline polymers (polyethylene, polypropylene, poly(butylene terephthalate) and Nylon 11) under oscillatory shear. Dynamic shear moduli (storage G′ and loss G″), loss tangent (tan δ), and dynamic viscosity (η′) were simultaneously, monitored during the crystallization process. The onset and completion of crystallization were characterized by the initial rise and final levelling off of G′, while the peak time, of crystallization (tp) is calculated from the time elapsed between the onset and peak of crystallization which is indicated by the G″ or η′ maximum. In the case of polypropylene, going from a low frequency of ≃0.1 rad/s, to higher frequencies of up to 10 rad/s, there is a monotonic decrease in peak time of crystallization (tp) together with a progressive decrease in spherulitic morphology. The observed acceleration in crystallization is due predominantly to the increase in nucleation rate and orientation of chains in melt crystalline aggregate. The progressive disappearance of the spherulitic morphology is attributed to the disruption of the spherulite superstructure at higher frequencies of shear. Copyright © 1979 Society of Plastics Engineers, Inc.