Cracking in polylactide spherulites



A polylactide of high optical purity was crystallized between 100 and 140 °C, in-between two glass slides, and its morphology was investigated by polarizing optical microscopy, scanning electron microscopy, and atomic force microscopy, during subsequent heating and cooling cycles between −15 °C and the crystallization temperature. It was found that dark circular rings show up on cooling on top of the spherulites and represent cracks of about 300 nm in width. This phenomenon is completely reversible, and the heating–cooling curves are centered at about 56 °C, which coincide with the Tg of polylactide. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3308–3315, 2005