Effect of a smectic liquid crystal polymer as new β-nucleating agent on crystallization structure, melting, and rheological behavior of isotactic polypropylene

Abstract

A smectic liquid crystal polysiloxane containing cholesteryl groups (SLCP-NA) was synthesized and used as a new kind of β-nucleating agent to induce the formation of β-crystal in isotactic polypropylene (iPP). The nucleating ability of SLCP-NA was investigated using wide-angle X-ray diffraction and differential scanning calorimetry. The content of SLCP-NA and crystallization temperature could lead to substantial changes to crystallization behavior of iPP. As the SLCP-NA content and crystallization temperature increased, the relative content of β-crystal (Kβ) tended to first increase and then decrease. The Kβ value reached a maximum value of 66.3% when the mass fraction of SLCP-NA and the crystallization temperature were 0.2 wt% and 120 °C, respectively. In addition, the rheological behavior of the iPP/SLCP-NA blends was studied. Exhilaratingly, a little mass fraction of SLCP-NA was found to greatly improve the flow ability of the blends, and the melt flow rate increased from 2.9 g/10 min of pure iPP to 43.9 g/10 min of the iPP blend with 0.3 wt% SLCP-NA. Moreover, the addition of SLCP-NA could decrease temperature sensitivity and increase shear sensitivity.