Does degraded or burned polymer seem to show up when you least expect it? If so, it's probably coming from one of your adapters or coextrusion flow pipes. While only very badly designed screws and dies will cause polymer to degrade during processing, the same cannot be said of adapters and flow pipes. Complicating matters is a design "catch 22" concerning these components. Typically they are designed to minimize pressure drop, yet minimum velocities must be maintained inside the flow channels to continuously clean the walls. These two design considerations are contradictory because the larger the channel, the lower the pressure drop—and the lower the velocity.
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