Dynamic Viscoelastic Properties of Long Organic Fibre Reinforced Polypropylene in Molten State

This paper deals with the dynamic viscoelastic properties of long organic fibre (aramid fibre (KF), polyvinyl alcohol fibre (VF) and polyamide fibre (PA6)) reinforced polypropylene in the molten state. Long organic fibres mixed with polypropylene fibres by an apparatus called a “fibre separating and flying machine^″ were compression moulded into 3mm thick composites. Dynamic viscoelastic properties of these composites were measured in the molten state using a rotational parallel plate rheometer. It was found that the dependence of angular frequency on storage modulus, G′, for long organic fibre reinforced polypropylene is different from that of volume fraction of fibre, V_f and the relationships depend on the characteristics of the reinforcing organic fibres. The slope of the dynamic viscosity, η′ vs. angular frequency, ω 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 increasing V_f in the same way as η′. 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, η* and complex modulus, G*. The yield value, G*_y increases gradually with increasing fibre content and approaches a fixed value. All of the long organic fibre reinforced polypropylenes studied here are more sensitive to temperature than inorganic fibre reinforced composites.