Journal of Cellular Plastics vol:52 issue:1 pages:107-130
A new micromechanical model that predicts anisotropic elastic properties of cell-wall material in nanoclay-reinforced polymeric foams is proposed. The model accounts for the reorientation of nanoclays during the foaming process, due to the stretching of the foam cell walls. Elastic moduli of bulk nanocomposites were studied first. It was found that given the high aspect ratio of nanoclays, they cannot be randomly placed in a representative volume element without having them intersect each other at high weight fractions. At 1.5 wt% the nanoclays already align and form clusters resulting in a significant effect on the stiffness of the nanocomposite. The number of silicate layers per cluster stack was also found to influence the Young’s modulus of the nanocomposite. When reinforcing polypropylene (PP) with 2 wt% of nanoclays, the modulus of elasticity decreased by 17% when the number of clays in a cluster went from 1 (fully exfoliated system) to 5. The stretching of the nanocomposite was shown to reorient nanoclays and, consequently, to change the stiffness of the cell wall. For the PP reinforced with 1 wt% of nanoclays and a stretching ratio of 6.5, the modulus increased by 15%.