CHARACTERIZATION OF FINITE-LENGTH COMPOSITES - PART VI - RHEOLOGICAL STUDIES OF MATERIALS BASED ON THE POLYPROPYLENE MATRIX

A range of rheological and morphological techniques, contributed by ni ne laboratories, are used to characterise the flow behaviour in a mode l long fiber reinforced thermoplastic system. It is concluded that in capillary rheometry, the pressure drop fluctuations that typify the fl ow arise from two mechanisms, that of local fiber fraction inhomogenei ty passing through the die, and the instability of the vortices in the die entry region which worsen as shear rate is increased. It is clear that the test geometry is significant in both capillary and torsional measurements. Yield stresses of 3.5 Pa (5 mm fiber length) and 7 Pa ( 10 mm fibres) have been evaluated.