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Journal of thermal analysis

, Volume 47, Issue 4, pp 941–955 | Cite as

Crystallization, melting and spherulitic structure of Β-nucleated random propylene copolymers

  • J. Varga
  • F. Schulek-Tóth
Article

Abstract

The characteristics of crystallization, melting and spherulitic growth of a random propylene copolymer (PRC) containing small amount of ethylene were studied in the presence of a selective Β-nucleating agent (calcium pimelate). It was established that the products of isothermal and non-isothermal crystallization are very rich in Β-modification but have mixed polymorphic composition. The formation of α-modification may be attributed to Βα-transition on the surface of growing Β-spherulites resulting in αΒ-twin-spherulites. During melting of PRC of Β-modification, the characteristics observed with Β-nucleated propylene homopolymers, namely, a Βα-recrystallization of recooled samples and separated melting of non-recooled samples (i.e. the melting memory effect), as well as a ΒΒ-recrystallization leading to a perfection of the structure within the Β-modification, are also demonstrated. The disturbance of regularity of the polymer chain highly reduces the tendency to Β-crystallization. In contrast to the observations with propylene homopolymers, the growth rate of α-modification (Gα) is higher than that of Β-modification (Gβ) and no critical crossover temperature can be found (T(Βα)=413 K) below whichGα>Gβ. The experimental results show that a partial disturbance of chain regularity by incorporation of comonomer units considerably reduces the tendency to Β-crystallization.

Keywords

characterization crystallization propylene copolymers 

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Copyright information

© Wiley Heyden Ltd., Chichester and Akadémiai Kiadó, Budapest 1996

Authors and Affiliations

  • J. Varga
    • 1
  • F. Schulek-Tóth
    • 1
  1. 1.Department of Plastics and RubberTechnical University of BudapestBudapestHungary

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