Isothermal crystallization kinetics of polypropylene latex-based nanocomposites with organo-modified clay

Abstract

The effect of organo-modified clay (Cloisite 93A) on the crystal structure and isothermal crystallization behavior of isotactic polypropylene (iPP) in iPP/clay nanocomposites prepared by latex technology was investigated by wide angle X-ray diffraction, differential scanning calorimetry and polarized optical microscopy. The X-ray diffraction results indicated that the higher clay loading promotes the formation of the β-phase crystallites, as evidenced by the appearance of a new peak corresponding to the (300) reflection of β-iPP. Analysis of the isothermal crystallization showed that the PP nanocomposite (1% C93A) exhibited higher crystallization rates than the neat PP. The unfilled iPP matrix and nanocomposites clearly shows double melting behavior; the shape of the melting transition progressively changes toward single melting with increasing crystallization temperature. The fold surface free energy (σ e ) of polymer chains in the nanocomposites was lower than that in the PP latex (PPL). It should be reasonable to treat C93A as a good nucleating agent for the crystallization of PPL, which plays a determinant effect on the reduction in σ e during the isothermal crystallization of the nanocomposites. The activation energy, ΔE a , decreased with the incorporation of clay nanoparticles into the matrix, which in turn indicates that the nucleation process is facilitated by the presence of clay.