MEASUREMENT OF MELT VISCOELASTIC PROPERTIES OF POLYETHYLENES AND THEIR BLENDS - A COMPARISON OF EXPERIMENTAL-TECHNIQUES

Two polyethylene resins (LDPE and HDPE) and their blends were characte rized for dynamic shear rheology, extrudate swell. in a capillary rheo meter, and recoverable strain as measured by the Melt Elasticity Index er in attempts to compare parameters related to the so-called ''melt e lasticity'' as obtained by different experimental techniques. Such par ameters may be useful in screening materials for their melt processabi lity. Data were obtained at equivalent shear rates/frequencies and dif ferent temperatures. With respect to the individual blend components, the LDPE resin with the lower Melt Index (MI) had higher storage modul us and Weissenberg number than the HDPE resin. However, by using crite ria based on ''recoil'' and strain recovery, ranking was different wit h the LDPE resin shown to exhibit lower ''melt elasticity.'' In this c ase, extrudate swell data were found to correlate reasonably well with equilibrium recoverable strain data. With respect to blends, complex viscosity and storage modulus versus composition curves showed positiv e deviations from Linearity, similar to those observed in melt heterog eneous blends. Similarities between the short time recoverable strain vs. composition and the storage modulus vs. composition curves suggest that similar morphological states may exist in the melt over the expe rimental times and conditions applicable to these different experiment al techniques.