Tuning the crystallization and polymorphic composition of polypropylene by organo-silane-modified silica

Abstract

This work investigates the influence of the alkyl chain length in organosilane-modified silica particles on the crystallization behavior and polymorphic composition of isotactic polypropylene (iPP). Using differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS), blends of iPP with both modified and unmodified SiO<inf>2</inf> particles were analyzed. The kinetics of isothermal crystallization was calculated as well. The results show that organosilane-modified silica promotes the formation of the β-phase, with its proportion increasing alongside the length of the alkyl chain. Besides, the polymorphic composition of iPP is significantly affected by cooling rate and crystallization temperature, with rapid cooling favoring β-phase formation. The highest β-phase content in iPP is achieved using silica modified with octadecyltriethoxysilane (C18) combined with rapid cooling or isothermal crystallization below 134 °C. Notably, these significant effects were achieved at a very low silica concentration of just 0.2 wt percent in the polymer matrix. The combination of Hoffman-Lauritzen theory and Avrami kinetics model was applied to study the influence of silica modification on crystallization kinetics: The effect on morphology proved to be greater than on the crystallization kinetics. This study provides insights into tailoring the crystallization and polymorphism of iPP via surface modification of filler particles in combination with setting of processing conditions.