CHARACTERISATION OF FINITE LENGTH COMPOSITES: Part VI-Rheological studies of materials based on the polypropylene matrix

A range of rheological and morphological techniques, contributed by nine laboratories, are used to characterise the flow behaviour in a model long fiber reinforced thermoplastic system. It is concluded that in capillary rheometry, the pressure drop fluctuations that typifl the flow arise from two mechanisms, that of local fiber fraction inhomogeneity 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.