Self‐organization of micro reinforcements and the rules of crystal formation in polypropylene nucleated by non‐selective nucleating agents with dual nucleating ability

Abstract

This work demonstrates and models the self-organization of mixed polymorps in polymers containing simultaneously growing phases with different growth rates. The model was verified and demonstrated in isotactic polypropylene nucleated by a nonselective nucleating agent. The crystallization and melting processes were studied by calorimetry (DSC) and polarized light microscopy (PLM). The morphology of the samples was investigated using PLM and scanning electron microscopy (SEM). The fundamental rules of the formation of two polymorphic modifications developing simultaneously on the same nucleating particle are introduced. A simple equation is suggested to predict the morphological geometry on the lateral surface of the nucleating agent. The results indicated good agreement between the predicted and observed geometry. The proposed model explains the self-organization of micro-sized reinforcements of α-modification in the matrix of β-iPP. Although the proposed equation was tested for this particular case it is a general equation for all structures in which different polymorphs are growing simultaneously with different growth rates.

Organogelators with dual β- and α-nucleating ability in isotactic polypropylene

“…These β-crystals develop simultaneously to the α-form, but they have faster growth rate and occlude the slower α-modification. This process had been reported in detail in our earlier studies [24,25]. The same tendency can be observed in random copolymer as well, which is presented in Fig.…”

“…The melting curves presented prove clearly that the nucleating agents have dual nucleating ability, so they induce the formation of the α-and the β-modifications at the same time [24,25,36]. In such a case, the polymorphic composition depends on the polymer structure, selectivity of the nucleating agent and on the thermal conditions like temperature range and cooling rate.…”

“…Other soluble nucleating agents are soluble β-nucleating agents having dual nucleating ability, for example N,N′dicyclohexyl-therephthalamide [24,25]. Accordingly, it induces the formation of the α-and the β-modifications as well.…”

“…The crystallization process in the presence of this non-selective and partially soluble nucleating agent is very complex, because the recrystallization of the nucleating agent as well as the formation and growth rates of the αand β-modifications depend on the temperature and all these parameters influence the final morphology. Consequently, various supermolecular structures with different final properties can develop in samples nucleated by such nucleating agents [24,26].…”

Effect of N,N′-Dicyclohexyldicarboxamide Homologues on the Crystallization and Properties of Isotactic Polypropylene

“… 22 The exact geometry can be calculated knowing the ratio of the growth rates of the two modifications. 23 Another decisive factor is the concentration of the nucleating agent. As these nucleating agents are only partially soluble, if their concentration increases, the temperature at which they start to recrystallize from the polymer melt also increases.…”