Temperature dependence of crystallization of nano-oriented crystals of iPP and the formation mechanism

We studied the formation mechanism of ‘nano-oriented crystals (NOCs)’ of isotactic polypropylene in elongational crystallization through crystallization temperature dependence of NOCs formation. We proposed a ‘chain reaction model’ of NOCs formation: The local oriented melt is formed by the melt elongation, which significantly accelerates nucleation; and, generated nuclei accelerate formation of local oriented melt that accelerates nucleation again. We obtained the nucleation rate (Iobs) of NOCs against the degree of supercooling (ΔT). Here, an equilibrium melting temperature in the oriented melt Tm0=220 °C is estimated from observation of NOCs formation. Iobs was well fitted by well-known equation of for homogeneous nucleation in classical nucleation theory, where C is a constant. Therefore, we concluded that NOCs formation is mainly controlled by the homogeneous nucleation process.