Competition between α and γ phases in isotactic polypropylene: effects of ethylene content and nucleating agents at different cooling rates

Crystallization kinetics of iPP: Influence of operating conditions and molecular parameters

“…19,[22][23][24] As for the b phase, it basically shows up only if specific b nucleants are added; therefore, for commercial non-bnucleated iPPs, it does not form [22][23][24] ; traces of g form crystals are often present, but always in minor amount and in a narrow window of operating conditions (i.e., cooling rates), hence its presence is neglected without affecting the reliability of the results. 19 Under the aforementioned hypotheses, as two different crystalline phases are formed (a and mesomorphic), at least two kinetic processes take place simultaneously. The simplest model is a parallel of two kinetic processes noninteracting and competing for the available molten material.…”

“…Different configurations (isotacticity and head-to-tail sequences) or addi-tion of small monomeric units and nucleating agents can also influence the final structure. [18][19][20][21][22][23][24][25] Influence of molecular weight on polymer crystallization is controversial. Stem length indeed interferes with entanglement density, thus determining a rate-controlled segregation regime of topological constraints in noncrystalline regions.…”

“…As a result of these counteracting effects, a relatively narrow window of cooling rates exists in which an enhancement of crystallization kinetics sets in. 19 A better understanding of the relation between processing and properties can be achieved if the absolute crystallinity during transformation can be predicted as a function of processing conditions. This prediction has to be supported by a crystallization kinetics model; in this article, a modified two-phase nonisothermal form of the Kolmogoroff-Avrami-Evans model was used to describe the crystallization kinetics.…”

Crystallization of α and γ Phases in Isotactic Polypropylene with Low Ethylene Content: Isothermal Crystallization and Secondary Crystallization

“…A large amount of it is obtained by crystallization under high pressure (11, 12), by using low molecular weight materials (13,14) and by co-polymerization with low content ethylene (13,(15)(16)(17)(18). The crystal structure of the phase had long remained a puzzle.…”

“…When IPP copolymer with low ethylene content is used, with increasing in ethylene content and in crystallization temperature, the crystals in the sample increase (18 x-ray experiment on IPP that the secondary crystallization occurrs during the growth of the spherulites and is strongest behind the growth front of the spherulites, that is, the conventional experiment may observe both the primary and the secondary crystallization processes at the same time.…”