Innovative polyethylene (PE) films are constantly being developed by switching the existing or incumbent resin with a new or challenger resin. If the extrusion equipment is designed properly, the film with the challenger resin will be acceptable for further testing and marketing. However, if the extrusion equipment is not designed properly, old degraded material from the incumbent resin will be pushed out of the extruder by the challenger resin, contaminating the test film. In many cases, the challenger resin incorrectly receives the blame for the gels. This paper describes the incumbent effect, presents a case study, and provides technical solutions.
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