A New High Sensitivity System to Detect Instabilities During the Extrusion of Polymer Melts

This publication is concerned with the development of a novel high sensitivity instability detection die for a laboratory size extruder. The high sensitivity system consists of piezoelectric transducers placed along the die length to monitor local pressure fluctuations, having temporal and pressure resolution of up to Δt ≈ 10−3 s and Δp ≈ 10−5 bar, at a nominal pressure of 500 bar. The system is tested on short chain branched polyethylenes, namely on the detection and characterization of the sharkskin instability. It is shown that the determined instabilities are related to characteristic peaks in the corresponding in situ pressure Fourier‐transform spectra and that other peaks are caused by different, but defined, sources. The in situ results obtained are validated through optical image analysis of the instabilities.