Dynamic viscoelastic properties of long organic fibre reinforced polypropylene in molten state

This paper deals with the dynamic viscoelastic properties of long organic f ibre [aramid fibre (KF), polyvinyl alcohol fibre (VF) and polyamide fibre ( PA6)) reinforced polypropylene in the molten state. Long organic fibres mix ed with polypropylene fibres by an apparatus called a "fibre separating and flying machine" were compression moulded into 3mm thick composites. Dynami c viscoelastic properties of these composites were measured in the molten s tate using a rotational parallel plate rheometer. It was found that the dep endence of angular frequency on storage modulus, G', for long organic fibre reinforced polypropylene is different from that of volume fraction of fibr e, Vf and the relationships depend on the characteristics of the reinforcin g organic fibres. The slope of the dynamic viscosity, eta' vs. angular freq uency, omega curves increases gradually up to 45 degrees with increasing V- f. Influence of fibre content on dynamic viscoelastic properties depends on the organic fibre used. For low fibre content, G' increases with increasin g V-f in the same way as eta', However, the opposite trend is observed for high fibre content composites. It can be deduced that there is an apparent yield from the relations between complex viscosity, eta* and complex modulu s, G*. The yield value, G*y increases gradually with increasing fibre conte nt and approaches a fixed value. All of the long organic fibre reinforced p olypropylenes studied here are more sensitive to temperature than inorganic fibre reinforced composites.