MELT FLOW INSTABILITIES OF FILLED HDPE

Data relating to the influence of several fillers on flow instabilitie s in capillary extrusion of two grades of high density polyethylene (H DPE) ave presented. Special attention is paid to the pressure oscillat ion region of the flow curve. First we show that a certain level of fl ow stabilisation can be achieved with carbon fibres, while carbon blac k and CaCO3 have a minor influence only on the oscillation effect when varying the filling between 5% and 10%. The temperature used was 200 degrees C and the capillary entrance was plane (180 degrees). We also show that a complete disappearance of pressure oscillations is obtaine d when using a different HDPE grade filled with 7% filmed silica or ca rbon black (also different grade). Compounds containing 7% talc did no t stabilise the flow. The same was true when the filling was reduced t o 3%. In the latter experiments a capillary rheometer with a conical e ntrance (120 degrees) was used. The temperature was 160 degrees C. Dat a obtained by frequency analysis of the fluctuating pressure transduce r signal mounted on the rheometric equipment, operating in both cases at constant piston speed, are also presented.