One barrel of the rheometer was fitted with a capillary die of L/D
ratio 16 and the other bore was fitted with an orifice die. The bore
diameter of both capillary dies was 1mm, with die entry angle of
180◦, whilst the lengthswere 16 and less than 0.25mmfor long and
orifice dies, respectively. Capillary dies were fitted into the bottom
of the barrels and pressure transducers located directly above the
dies. The capillary dies were made from tungsten carbide–cobalt
alloy in order to maintain tight geometrical integrity.
The polymer was dried in an oven at 50 ◦C for 24 h before rheological
investigation. The flow behaviour of each grade of HPC
was characterised at 140, 145 and 150 ◦C. The rheometer was set
at test temperature and allowed to stabilize. Temperatures were
controlled within ±0.5 ◦C of the set values and monitored by platinum
resistance thermometers fitted in the three (top, middle and
bottom) zones of the barrel. The polymer was fed into both bores
of the barrel and manually compressed before the test was started.
The polymerwas subjected to pre-compression pressure of 0.5MPa,
and a total pre-heating time of 240 s. The instrument was run in
8-stage discrete speed programme. The piston speedwas automatically
converted to shear rate by software and is summarised in
Table 1.
One barrel of the rheometer was fitted with a capillary die of L/Dratio 16 and the other bore was fitted with an orifice die. The borediameter of both capillary dies was 1mm, with die entry angle of180◦, whilst the lengthswere 16 and less than 0.25mmfor long andorifice dies, respectively. Capillary dies were fitted into the bottomof the barrels and pressure transducers located directly above thedies. The capillary dies were made from tungsten carbide–cobaltalloy in order to maintain tight geometrical integrity.The polymer was dried in an oven at 50 ◦C for 24 h before rheologicalinvestigation. The flow behaviour of each grade of HPCwas characterised at 140, 145 and 150 ◦C. The rheometer was setat test temperature and allowed to stabilize. Temperatures werecontrolled within ±0.5 ◦C of the set values and monitored by platinumresistance thermometers fitted in the three (top, middle andbottom) zones of the barrel. The polymer was fed into both boresof the barrel and manually compressed before the test was started.The polymerwas subjected to pre-compression pressure of 0.5MPa,and a total pre-heating time of 240 s. The instrument was run in8-stage discrete speed programme. The piston speedwas automaticallyconverted to shear rate by software and is summarised inTable 1.
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