Ultrasonic characterization of polymer melts under processing conditions

摘要

A method and apparatus for ultrasonically characterizing a polymer melt flowing in a predetermined direction between two opposed parallel surfaces spaced from one another to define a gap filled with polymer are disclosed. Ultrasonic pulses are propagated through the polymer melt between the two surfaces in a direction normal to the direction of flow for interaction with the polymer, the ultrasonic pulses having a duration such as to prevent successive echoes from overlapping with one another while reverberating between the two surfaces. The time delay between two echoes exiting from the polymer melt and generated from each pulse having interacted with the polymer is continuously monitored while simultaneously monitoring amplitude variations of the two echoes, to provide output signals representative of ultrasonic velocity and attenuation in the polymer melt. These output signals are processed to obtain data comprising ultrasonic velocity and attenuation values measured simultaneously as a function of time. The data is then processed to derive quantitative information relating to viscoelastic properties, structure or composition of the polymer, which can be used as input data in a closed-loop process control system.