Comparison of shear-induced crystallization behavior of PB-1 samples with different molecular weight distribution

Abstract

Shear-induced crystallization behavior of three grades of PB-1 having different molecular weights and breadths of molecular weight distribution was investigated by means of rotational rheometry covering a shear rate range of 0.0001 up to 0.3 s−1 and temperatures between 99 °C and 107 °C. The up-shoot in viscosity after a certain time is used to define an onset time ton for both quasiquiescent and shear-induced crystallization. The plot of ton versus the shear rate can be converted into a temperature-invariant curve by dividing the y axis by quiescent onset time ton,q and multiplying the x axis by the square root of ton,q. The shape and location of the T-invariant curves for the three PB-1 samples are compared with respect to their molecular parameters. An additional normalization step by multiplying the abscissa by the square root of the characteristic retardation time of the melt yields a dimensionless representation of the T-invariant curve. Furthermore, by this procedure the three curves are shifted into one region, where they have the same threshold value, indicating the onset of shear-induced crystallization. A connection of this T-invariant curve to the morphology of the crystallites formed are addressed.