Capillary Flow of Polypropylene Melt

Abstract

A parameter representing Barus effect, flow broadening effect, (dmax/d0) was measured for different capillaries of same diameter (d0=0.45mm) ranging in the length l on polypropylene melt (Mv=2.39×105) at 250°C, where dmax is the maximum diameter of the extruded filaments. The apparant shear modulus obtained from Spencer-Dillon's plots depended on the die-dimension and the extrapolated shear modulus in the limit of l/d0→0 was 5.6×105 dyne/cm2 Plots of {(dmax/d0)2-1} vs. mean passing time through die (Ziabicki plot) showed the curvature contrary to his prediction. The following (dmax/d0)-internal stress Si relation was proposed, _??_where, E: the Young modulus, Δ: a parameter representing the contribution of the chain orientation to (dmax/d0).(dmax/d0) decreased with l towards an asymptotic limit at 2l/d0=30, which was designed as Δ. The good agreement of experimental data with the above equation confirms the validity of proposed mechanism, i. e., one-dimentional elongation at die inlet and successive relaxation during passing through die, in addition to the orientation effect.Δ increased linearly with increasing shear stress. The approximate constant d log Q/d log τ=-1 was obtained, where Q, flow rate in cm3/sec, τ relaxation time of internal stress in sec.