Rheological comparison of three polyethylene film resins

Several rheological tests have been carried out on low density, film‐grade polyethylenes manufactured by three Canadian companies. The resins all have densities around 0.92, but are made by different processes. The Union Carbide resin is made in a tubular reactor, the C.I.L. resin in a two‐stage autoclave and the DuPont of Canada resin by means of a low pressure copolymerization process. The shear viscosity was determined for each resin over a wide range of shear rates at several temperatures, and the first normal stress difference was determined at low shear rates. Die swell was measured at the higher shear rates. The low‐pressure copolymer was found to be quite similar in its behavior to the resin made in a high pressure autoclave. Correlations between the various properties measured, proposed by Abdel‐Khalik et al (7) on the basis of the Goddard‐Miller constitutive equation (8) , were tested and found not to be obeyed. A method proposed by Tanner for calculating die swell from the viscometric functions is also evaluated.