Effect of shear stress on crystallization of isotactic polypropylene from a structured melt

摘要

Experimental results about the effect of shear stress generated at the wall of a capillary leading to the formation of iPP cylindrites in connection with bundles of partially ordered chain segments required for the generation of orientation in a NMP structured melt was reported. For a given structured melt, the number of cylindrites increased with shear stress. As a result, the nucleation density of α-iPP within a single cylindrite structure increased with shear stress at the expense of β-iPP nucleation density. In-situ SAXS and WAXS measurements indicate that nanoscale ciliated bundles of partially ordered chain segments were produced by controlling the melt structure in a quiescent near melting point melts of iPP. The SAXS patterns of NMP melt monitored at 180°C can be fitted by using a form factor for polydisperse cylinders. Cylindrites were generated by applying shear stress of different magnitude during the flow of a NMP structured melt.