Thermal characterization of polycarbonate/polycaprolactone blends

In this work, we prepared blends of bisphenol A polycarbonate (PC) and poly (epsilon -caprolactone) (PCL) in a wide composition range by melt mixing an d solution mixing. Two different molecular weights of PCL were used (nomina lly, 10.000 g/mol, PCL10, and 80.000 g/mol, PCL80). The thermal behavior of both systems was studied via differential scanning calorimetry under dynam ic and isothermal conditions. The blends were miscible in the entire compos ition range in the liquid and amorphous states, as indicated by the single glass-transition temperature (T-g) exhibited by both the PC/PCL10 and PC/PC L80 blends. The compositional variation of the T-g was accurately described by the Fox equation for the PC/PCL80 blends, whereas slight deviations fro m this equation were exhibited by the PC/PCL10 blends. For blend compositio ns containing 40% or more PCL, either one or both blend components crystall ized. Crystallization occurred during cooling from the melt or during subse quent heating in the form of cold crystallization. Although PCL crystalliza tion was reduced and its crystallization rate decreased with the addition o f PC, PCL was a very effective macromolecular plasticizer for PC, to the ex tent that crystallization during the scan was detected for some blend compo sitions. Isothermal crystallization experiments allowed the determination o f equilibrium melting points (T-m(o)) by the Hoffman-Weeks extrapolation me thod. A T-m(o) depression was found for both PCL and PC components as the c ontent of the other blend component was increased. The Avrami equation was closely obeyed by both blend components during the isothermal overall cryst allization kinetics up to crystalline conversion degrees of 60-70% and with values of Avrami indices ranging from 3 to 4, depending on the crystalliza tion temperature employed. (C) 2001 John Wiley & Sons, Inc.