Component redistribution in extrusion of polyethylene compounds^†

Calorimetrically determined integral heats of solution and swelling ratio measurements carried out on extrudates of low-density polyethylene blended with Surlyn ionomer and ethylene–ethyl acrylate copolymer provide independent evidence for the redistribution of components as a result of extrusion. Although this evidence for “migration” supports earlier data for extrusion-triggered molecular redistribution in polyethylene, the present data further suggest that the effect may be due at least in part to the tendency of crystallizable polydisperse polymers to form cohesively weak boundary layers upon cooling from the melt. Thus, molecular redistribution effects may be expected in the processing of polyethylene and related thermoplastics but would not be pronounced in the extrusion of amorphous, narrow molecular weight distribution polymers, e.g., polystyrene.