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Structure, morphology and crystallization of a random ethylene-propylene copolymer (Articolo in rivista)

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Structure, morphology and crystallization of a random ethylene-propylene copolymer (Articolo in rivista) (literal)

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Silvestre C., Cimmino S., Triolo R. (2002)
Structure, morphology and crystallization of a random ethylene-propylene copolymer
in Journal of polymer science. Part B, Polymer physics; WILEY-LISS, DIV JOHN WILEY & SONS INC, 111 RIVER ST, HOBOKEN, NJ 07030 (Stati Uniti d'America)
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Polypropylene random copolymers constitute an important class of plastic resin, particularly suitable for the packaging industry to be transformed in films with a satisfying balance of clarity, flexibility and mechanical strength. Recent market trends are towards products with increasingly lower heat sealing initiation temperatures, allowing faster and more economic processing. This property belongs to the copolymers and is mainly related to the melting temperature, which decreases with the insertion of the comonomer along the polymer chain. The introduction of second comonomer along with propylene segments, in fact, promotes the formation of shorter stereoregular blocks, which melt at a lower temperature. Impact factor 2004: 1.369 (literal)

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No. Citazione=3; Autocitazione=0; Motore utilizzato per le citazioni=Google Scholar. (literal)

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With this work we gave a contribution to the definition of the polymorphism behaviour of ethylene-propylene copolymer, as well as the overall morphology in dependence of preparation conditions, as cold crystallization, and during annealing starting from the cold state, that control the final optical, mechanical and physical properties. The analysis of the structural results suggests that g-phase of isotactic polypropylene (iPP) could be generated for high molecular mass samples decreasing drastically the undercooling and that the structure of the smectic phase is close to that characterizing the monoclinic orm structure. The spherulite growth rate data, obtained by using the procedure suggested by Chung and Chen and modified by Silvestre et al., demonstrate that the presence of ethylene sequences decreases the spherulite growth rate, G, at given Tc. This decrease is for the first time related not only to rejection of the ethylene sequences from the growth front, but also to the formation of different crystals, having different crystallization kinetics. It is hypothesized that at atmospheric pressure and Tc, between 110- 128°C, the different polymorphs have different crystallization growth rate and in particular Gg< Ga

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Istituto di Chimica e Tecnologia dei Polimeri Università Palermo, Dipartimento Chimica Fisica,Via le delle Scienze, Parco d'Orleans II, 90128 Palermo, Italy (literal)

Titolo

Structure, morphology and crystallization of a random ethylene-propylene copolymer (literal)

Abstract

Structure, morphology and crystallization behaviour of a random ethylene-propylene copolymer, containing 2% in weight of ethylene sequences, are analyzed and compared with those of a plain polypropylene sample, by means of optical and scanning microscopy, wide angle x ray scattering and calorimetry. For the copolymer, different polymorphs (alfa, gamma and smectic modification) and morphologies can be obtained changing crystallization and annealing conditions. The analysis of the structural results suggests that gamma-phase of isotactic polypropylene (iPP) could be generated for high molecular mass samples decreasing drastically the undercooling. The spherulite growth rate data in dependence on Tc are obtained by using the procedure suggested by Chung and Chen and modified by Silvestre et al. The results demonstrate that the presence of ethylene sequences decreases the spherulite growth rate, G, at given Tc. It is hypothesized that at atmospheric pressure and Tc, ranging between 110-128°C, the different polymorphs have different crystallization growth rate and in particular Ggamma < Galfa < Gbeta. (literal)

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