Effects of Melt Structure on Shear-induced Crystallization of Isotactic Polypropylene

B. Zhang and J. B. Chen

School of Materials Science & Engineering, Zhengzhou University, Zhengzhou 450002, People’s Republic of China

Based on a control of the melt structure at temperatures near but below the equilibrium melting point we investigated the role of shear stress imposed by the wall of the capillary die on crystal morphology of isotactic polypropylene (iPP). Bundles of partially ordered nanoscale chain segments within the quiescent melt at temperatures between the nominal melting temperature and the equilibrium melting point allowed for the possibility of shear-induced or shear-assisted formation of crystalline cylindrites which were investigated by means of polarized optical microscopy and small/wide-angle X-ray scattering.1-4 The SAXS patterns of near melting point structured melt monitored at 180 °C can be fitted by using a form factor for polydisperse cylinders. It was found that the average radius and height of the bundles of partially ordered chain segments were about 17 nm and 40 nm, respectively. For a given structured melt, the number of cylindrites increased with shear stress. Concomitantly, the nucleation density of α-iPP within a single cylindrite structure increased with shear stress at the expense of β-iPP nucleation density.

[1] Zhang, B.; Chen, J.; Zhang, X.; Shen, C. Polymer 52, 2075 (2011). (link)
[2] Zhang, B.; Chen, J.; Ji, F.; Zhang, X.; Zheng, G.; Shen, C. Polymer 53, 1791 (2012).  (link)
[3] Zhang, B.; Chen, J.; Cui, J.; Zhang, H.; Ji, F.; Zheng, G.; Heck, B.; Reiter, G.; Shen, C. Macromolecules 45, 8933 (2012). (link)
[4] Zhang, B.; Wang, B.; Chen, J.; Shen, C.; Reiter, R.; Chen, J.; Reiter, G. Macromolecules 49, 5145 (2016). (link)