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CPP: Chemische Physik und Polymerphysik

CPP 12: Crystallization in Polymers

CPP 12.4: Vortrag

Donnerstag, 5. April 2001, 16:45–17:05, 111

VITRIFICATION AND DEVITRIFICATION OF THE RIGID AMORPHOUS FRACTION OF SEMICRYSTALLINE POLYMERS REVEALED FROM FREQUENCY DEPENDENT HEAT CAPACITY — •Andreas Wurm and Christoph Schick — University of Rostock, Dept. of Physics, Universitaetsplatz 3, 18051 Rostock, Germany

For semi-crystalline polymers the relaxation strength at the glass transition shows significant deviations from a two-phase model. Introduction of a rigid amorphous fraction (RAF), which is non-crystalline but does not participate in the glass transition, allows a description of the relaxation behavior. The question arises when does this amorphous material vitrify. TMDSC measurements allow for the online study of heat capacity changes during isothermal crystallization. For Bisphenol-A Polycarbonate (PC) and poly(3-hydroxybutyrate) (PHB) changes in base-line heat capacity can be studied. The amount of RAF obtained at the crystallization temperature was compared with that obtained from the step in heat capacity at the glass transition at lower temperatures. No changes in the amount of the RAF occur in the temperature range between crystallization and glass temperature. Consequently, the rigid amorphous material is in total established during the isothermal crystallization of PC and PHB. This way crystallization in PC and PHB limits itself by vitrifying the crystallizable material next to the growing crystals. On heating devitrification of the RAF occurs when the crystals, which were formed last, melt in the temperature range of the lowest endotherm.