?- and ?-crystalline forms of isotactic polypropylene investigated by nanoindentation

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