6533b874fe1ef96bd12d6314

RESEARCH PRODUCT

Rheological Properties of Different Film Blowing Polyethylene Samples Under Shear and Elongational Flow

subject

description

Summary: The rheological behavior of polyethylenes ismainly dominated by the molecular weight, the molecularweight distribution and by the type, the amount and thedistribution of the chain branches. In this work a linearmetallocenecatalyzedpolyethylene(m-PE),abranchedme-tallocene catalyzed polyethylene (m-bPE), a conventionallinear low density polyethylene (LLDPE) and a low densitypolyethylene (LDPE) have been investigated in order tocompare their rheological behavior in shear and in elonga-tional flow. The four samples have similar melt flow indexand in particular a value typical of film blowing grade.The melt viscosity has been studied both in shear and inisothermal and non-isothermal elongational flow. The mostimportant features of the results are that in shear flow the m-PE sample shows less pronounced non Newtonian behaviorwhile in the elongational flow the behavior of m-PE is verysimilar to that of the linear low density polyethylene: thenarrowermolecularweightdistributionandthebetterhomo-geneity of the branching distribution are reasonably respon-sible for this behavior. Of course the most pronounced non-linear behavior is shown, as expected, by the LDPE sampleandbythebranchedmetallocenesample.Thissimilarbehav-ior has to be attributed to the presence of branching. Similarcomments hold in non-isothermal elongational flow; theLDPE sample shows the highest values of the melt strengthand the other two samples show very similar values. As forthe breaking stretching ratio the opposite is true for LDPEwhile m-PE and LLDPE show higher values. The transientisothermal elongational viscosity curves show that the bran-ched samples show a strain hardening effect, while LLDPEand m-PE samples present a linear behavior.Dimensionless flow curves of different polyethylenesamples.