Differential Scanning Calorimetry (D5.c.) and Optical Micr05COpy bave been used in order lo assess the influence of molecular weight and molecular weight distnbution (MWD) on thermal behavior and crystaIlization process of isotactic polypropylene (iPp) samples, all characterized by very lùgh isotacticity index (98 wl"). 1be values of lhe equilibrium melting temperature (f .J and surface free energy of folding (a.) of iPP Iamellar crystals have been determined aa:ording to the kinetic theory of polymer crystallization. Such lhermodynamic parameters were found lo increase with increasing iPP molecular weight, for a given iPP MWD and to decrease with inc:reasing iPP MWD, for a given iPP molecular weighl Also the values of the radial growth rale of iPP spherulites and nucleation density were found to be affected noticeably by molecular weight and MWD of iPP. For a given undercooling, 61, G decreases strongly with increasing iPP molecular weighl On the other hand faster nucleation was shown by iPP samples with comparatively lower molecular weight and broader MWD.
|Titolo:||Influence of molecular weight and molecular weight distribution on crystallization and thermal behaivour of isotactic polypropilene|
|Data di pubblicazione:||1995|
|Appare nelle tipologie:||1.1 Articolo in rivista|