Melt-state elongational rheometry of mineral-filled polyethylene

A free-surface elongational rheometer has been further developed to study t he melt state deformation and rupture behaviour of high-density polyethylen e (HDPE) polymers, and corresponding elasticity characteristics. An upgrade d, PC-interfaced data collection system has been introduced, appropriately calibrated to provide rapid and accurate data collection when tests are car ried out at high extensional strain rates; good agreement has been obtained between experimental and theoretical displacements, over a range of strain rates (0.1-6.0 s (-1)). Deformation (extensional stress-strain) response o f HDPE is shown to be sensitive to molecular weight, with low molar mass gr ades suffering melt rupture at Hencky strains between 2.0 and 3.0. Incorpor ation of inorganic calcium carbonate filler increases transient-state exten sional viscosity and rupture stress, but reduces the extensional strain at failure. The degree of elastic recovery is dependent upon the total elongat ional strain developed during the test; calcium carbonate-filled HDPE melts exhibit lower recovery at a given strain, but elasticity is enhanced when fatty-acid coatings are used to assist filler dispersion in the compound. ( C) 2000 Elsevier Science Ltd. All rights reserved.