posted on 2009-02-13, 13:53authored byBarry Haworth, Suparat Jumpa
Free surface elongational flow properties, including transient state stress
growth and melt rupture data, have been measured on a range of calcium
carbonate filled high density polyethylene (HDPE) compounds, using a
Rutherford elongational rheometer operating at constant strain rate in
the range 0·1–6·0 s−1. Results show that polymer molecular weight has a
strong influence on both tensile stress growth and melt rupture data; increasing
elongational strain rate decreases the stress growth coefficient,
in all compounds. At any specific elongational strain rate, the stress growth
coefficient increases with volume fraction of particulate additives and also
when using additives of fine particle size, as a result of packing fraction effects.
Acid coatings added at super-monolayer levels influence the viscosity of highly
filled compounds, by internal lubrication.
Dynamic extrusion data obtained by experimental blow moulding of calcium
carbonate modified HDPE materials show that modifications to melt state
shear modulus result in reduced die swell, to an extent determined by filler
coating. In combination with die swell, higher extensional viscosity of filled
HDPE contributes significantly to enhanced parison sag resistance. Solid state
modulus enhancement was consistently observed in calcium carbonate filled
HDPE containers and if excellent filler dispersion can be achieved, it is feasible
to retain the ductile mode failure of unfilled HDPE when containers are
subjected to high velocity impact loads.
History
School
Aeronautical, Automotive, Chemical and Materials Engineering
Department
Materials
Citation
HAWORTH, B. and JUMPA, S., 1999. Extensional flow characterisation and extrusion blow moulding of high density polyethylene modified by calcium carbonate. Plastics, Rubber and Composites, 28 (8), pp. 363-378