Multiple melting behavior of poly(butylene succinate). II. Thermal analysis of isothermal crystallization and melting process

Abstract

AbstractThe multiple melting behavior of poly(butylene succinate) (PBSu) was studied with differential scanning calorimetry (DSC). Three different PBSu resins, with molecular weights (MWs) of 1.1 × 105, 1.8 × 105, and 2.5 × 105, were isothermally crystallized at various crystallization temperatures (Tc) ranging from 70 to 97.5 °C. The Tc dependence of crystallization half‐time (τ) was obtained. DSC melting curves for the isothermally crystallized samples were obtained at a heating rate of 10 K min−1. Three endothermic peaks, an annealing peak, a low‐temperature peak L, and a high‐temperature peak H, and an exothermic peak located between peaks L and H clearly appeared in the DSC curve. In addition, an endothermic small peak S appeared at a lower temperature of peak H. Peak L increased with increasing Tc, whereas peak H decreased. The Tc dependence of the peak melting temperatures [Tm(L) and Tm(H)], recrystallization temperature (Tre), and heat of fusion (ΔH) was obtained. Their fitting curves were obtained as functions of Tc. Tm(L), Tre, and ΔH increased almost linearly with Tc, whereas Tm(H) was almost constant. The maximum rate of recrystallization occurred immediately after the melting. The mechanism of the multiple melting behavior is explained by the melt‐recrystallization model. The high MW samples showed similar Tc dependence of τ, and τ for the lowest MW sample was longer than that for the others. Peak L increased with MW, whereas peak H decreased. In spite of the difference of MW, Tm(L), Tm(H), and Tre almost coincided with each other at the same Tc. The ΔH values, that is crystallinity, for the highest MW sample were smaller than those for the other samples at the same Tc. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2039–2047, 2005