An Automatic Measurement of Density of Polyethylene

Abstract The density, p, is a very important parameter for the characterization of polyethylenes (PE). Usually, p, is measured using a density gradient column, on a small piece taken from a plaque which is prepared according to ASTM standards. Here we present a new technique of measuring the density of PE, which is based on the propagation of ultrasonic waves in the standard (ASTM) plaques of PE. While the acoustic method has an accuracy equivalent to that of the standard method, it also possesses a number of advantages: it is easy to use, foolproof, reliable, repetitive and nondestructive. Above all, the measurement is automatic and rapid (30 sec.). The basic principle of the measurement will be described and results will be shown. The theoretical foundation will be discussed on the grounds of a model for the elastic moduli of multiphase media.