α- and β-crystalline forms of isotactic polypropylene investigated by nanoindentation

Under special crystallization conditions from the melt, both alpha- and beta-forms of isotactic polypropylene were produced simultaneously. The alpha- and beta-spherulites of polypropylene were differentiated under optical microscope, allowing the nanoindentation of individual spherulites of each crystallographic form. Elastic modulus and hardness of beta-spherulites were found to be 10 and 15% respectively lower than in alpha-spherulites. The higher stiffness of alpha may be related to the particular interlocked structure with cross-hatched lamellae, and to a lower molecular mobility in the crystallites. (C) 1999 John Wiley & Sons, Inc.