Isothermal crystallization kinetics in the miscible blend system isotactic/atactic poly(fl-hydroxybutyrate) (PHB) are examined by optical microscopy. The presence of the atactic component results in a reduction in spherulitic growth rate of the isotactic polymer. Analysis of the growth rates using the Lauritzen-Hoffman model shows that a regime II~III transition is present for all blend compositions investigated (0-50wt% atactic), and that this transition occurs at a constant temperature of 140°C. The ratio of the nucleation constants for the two regimes, -K=g I n//-l=(gI,I is found to deviate from the theoretical value of 2.0 in the blend system. It is shown that a modified version of the Lauritzen-Hoffman equation incorporating entropic effects is unable to account for these deviations. The work of chain-folding, q, is calculated to be 5.1 kcal molfor isotactic PHB. The implications of using assumed values of the transport parameters in the kinetic analysis are discussed.
Посилання на статтю:
Crystallization kinetics in blends of isotactic and atactic poly(fl-hydroxybutyrate) / R. Pearce, G. R. Brown and R. H. Marchessault* // Polymer. – 1994. – Vol 35. – P. 3984-3989.