alpha- and beta-crystalline forms of isotactic polypropylene investigated by nanoindentation

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