Real-time observations of the kinetics and developing morphology of spherulites of a polyethylene copolymer

The morphology and kinetics of developing large spherulites of a metallocene-catalyzed linear-low-density polyethylene have been investigated in real time with polarizing optical microscopy. In contrast to the widely held view that lamellae advance smoothly into the melt, the isothermal growth rate of an individual radial unit fluctuates in space and time. There is also an overall continuing fall below the initial value with increasing radial distance as segregation proceeds and segregants accumulate. In the later stages of growth the morphology becomes increasingly irregular: some individual radial units may stop while others overtake them from the rear. Gross changes of direction occur to avoid certain regions which may be ∼10 μm across, consistent with high concentrations of segregants, indicate that local conditions at the melt interface vary strongly even when growth is slow.