Kinetics of competitive crystallization of β- and α-modifications in β-nucleated iPP studied by isothermal stepwise crystallization technique

Crystallization kinetics of beta-nucleated isotactic polypropylene (beta-iPP) under isothermal conditions were investigated by differential scanning calorimetry. iPP was nucleated by a trisamide derivative, namely tris-2,3-dimethyl-hexylamide of trimesic acid (TATA). In the presence of TATA possessing dual nucleating ability, the formation of the alpha- and beta-form occurs simultaneously. An isothermal stepwise crystallization method is suggested in this study, which can separate the crystallization process of beta- and alpha-iPP and consequently their crystallization kinetics can be evaluated separately. The results indicated that the mechanism of crystallization changes in temperature especially in the vicinity of the upper critical temperature of the formation of the beta-phase. In addition, it was found that the ratio of the growth rates of beta- and alpha-modification determines the characteristics of crystallization and influences the apparent rate constant of crystallization of both polymorphs.