Recrystallization of Quenched β-Form Isotactic Polypropylene Lamellar Crystals in Thin Films

The melting–recrystallization characterizations of quenched β-form isotactic polypropylene (β-iPP) lamellar crystals in ultrathin films were investigated via the self-seeding method. We found lath-like shaped α-iPP crystals generated within the region occupied by the initial β-iPP lamellae and calculated their average number density (Nα). Intriguingly, two slopes were derived from the semi-logarithmic plot of Nα versus partial melting temperature (Ts), which reflects that Nα is determined by βα-recrystallization and αα-recrystallization as Ts is below and above 157 °C, respectively. Furthermore, our experimental observations clearly demonstrate that two phase selection pathways, that is, ββ- and βα-recrystallization, are possible upon melting of the quenched β-iPP lamellae. In particular, we found that ββ-recrystallization emerges as the preferred route for the case of an initial β phase with sufficiently high thermal stability, which is probably thermodynamically controlled rather than kinetically controlled. Otherwise, βα-recrystallization will be the dominant process due to the growth kinetics.