Cracking in polylactide spherulites

A polylactide of high optical purity was crystallized between 100 and 140 degrees 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 similar to 15 degrees 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 degrees C, which coincide with the T-g of polylactide. (c) 2005 Wiley Periodicals, Inc.