Effects of Crystallization on Micromechanical Behavior of Polyethylene Nanocomposites

The addition of small amounts of nanofillers to a polymer matrix has been shown to impart significant changes in mechanical, dielectric, and optical properties. A common challenge in creating these polymer nanocomposites (PNCs) is controlling the dispersion of the nanofillers. Recent work has demonstrated methods to control dispersion and organization of spherical nanoparticles (NPs) in compatible matrices. At sufficiently slow crystallization rates in semicrystalline polymers, the NPs organize in the amorphous regions of the growing spherulites. PNCs with organized NPs have been shown to exhibit improved bulk mechanical properties, but the micromechanical behavior underpinning these has not been fully explored. In this study, in-situ Raman spectroscopy was performed on polyethylene samples under tensile load to explore differences in micromechanical behavior between neat, filled but unorganized PNCs, and PNCs with crystallization-induced particle organization. Crystallization of each sample was characterized in DSC, and organization of PNC samples confirmed by SAXS and TEM. Results show that the addition of fillers leads to a significant change in the distribution of load between the crystalline and amorphous phase. Shift is only apparent in samples that undergo necking (high strain), consistent with previous work on neat polyethylene.