Study of the rheological properties and crystallization behavior of branched PP/silicate composites

Abstract

Long-chain branched-polypropylene (LCB-PP) was prepared by melt grafting, and LCB-PP/silicate composites were prepared by adding 1–7 wt% silicate using a mini-compounder at 190 °C. The chemical structure of the LCB-PP was confirmed by the existence of a –C=C–H-stretching peak at 3100, cm−1 in the Fourier transform infrared spectrum. LCB-PP and the LCB-PP/silicate composites exhibited unusual rheological properties, including high shear-thinning tendency and elasticity. Shear-thinning tendency and elasticity were highest in the composite containing 5 wt% silicate. These effects were confirmed by oscillatory rheological measurements. The crystallization behavior of LCB-PP and the silicate composite were investigated using a non-isothermal process proposed by Ozawa. The exothermic pattern of the composite is narrower and sharper than those of PP and branched PP. The extending exponents were 3.6 for PP, 2.4 for LCB-PP and 1.5 for the composite. These behaviors can be interpreted by speculating that the silicate in the PP matrix functions as a seed for crystallization and alters the crystallization process. The slopes of G″–G′ decreased to 1.21 for the long-chain branched-polypropylene (LCB-PP) and 1.07 for PP-F07-S5. A decreased slope indicates an increase in elasticity, shear thinning effect and melt strength. The extending Avrami analysis proposed by Ozawa applied to PP, LCP-PP and the composite. The exponents were 3.6 for PP, 2.4 for LCB-PP and 1.5 for the composite.