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Pressure Variation during Interfacial Instability in the Coextrusion of Low Density Polyethylene Melts by M. T. Martyn; P. D. Coates is a Materials Science article available to read on EtoBox.

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## Abstract Pressure variation during the coextrusion of two low density polyethylene melts was investigated. Melt streams were delivered to a die from two separate extruders to converge in a 30°° geometry to form a two layer extrudate. Melt flow in the confluent region and die land to the die exit was observed through side windows of a visualisation cell. Stream velocity ratio was varied by control of extruder screw speeds. Layer thickness ratios producing wave type interfacial instability were quantified for each melt coextruded on itself and for the combined melts. Stream pressures and screw speeds were monitored and analysed. Wave type interfacial instability was present during the processing of the melts at specific, repeatable, stream layer ratios. Increased melt elasticity appeared to promote this type of instability. Analysis of process data indicates little correlation between perturbations in extruder screw speeds and stream pressures. The analysis did however show covariance between the individual stream pressure perturbations. Interestingly there was significant correlation even when interfacial instability was not present. We conclude that naturally occurring variation

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Author

M. T. Martyn; P. D. Coates

Publisher

Walter de Gruyter GmbH

Published

2013

Language

EN

Field

Materials Science (Physical Sciences)