Microstructure and Properties of Polypropylene/Clay Nanocomposites

Nanocomposites of polypropylene (PP) containing various contents of Cloisite 15A nanoclay particles were prepared by one-step melt compounding in a twin screw extruder. Tensile and impact properties of the nanocomposite systems were investigated and correlated with their microstructures. The tensile modulus increased with an increase in Cloisite 15A content but the tensile strength, elongation at break, and impact strength were decreased. WAXS and TEM studies showed almost exfoliated structures. There was a decrease in permeability values with an increase in nanoclay content up to 5wt. %. Exceeding this content of nanoclay had no significant effect on permeation due to the aggregation phenomenon at high concentrations of the nanoparticles. Most of the examined micromechanical models for prediction of the tensile modulus of the nanocomposite were successful despite being based on fiber-shaped fillers. An exfoliated structure of clay within the nanocomposite was assumed for the modeling using a molecular dynamics simulations approach, employing Dreiding, Forcite, and COMPASS force fields, in order to investigate the best one for a successful estimation of elastic modulus. Relative to the experimental modulus values of the nanocomposites, which were around 1100-1200MPa, the COMPASS force field had the best correlation with the values with a slight departure of about 10%.