The Solidification Behavior of a PBT/PET Blend Over a Wide Range of Cooling Rate

In recent years, much attention has been paid to the development of high-performance polyester blends, among which blends of polybutylene terephtha- late/polyethylene terephthalate (PBT/PET) are expected to exhibit remarkable prop- erties as far as their crystallization behavior is concerned. Through trial and error, appropriate commercial compositions have been chosen which could not be otherwise explained by a suitable interpretation of the mechanisms determining their solidifica- tion behavior. The solidification behavior of a 60/40 w/w PBT/PET blend was studied in a wide range of cooling conditions, according to a continuous cooling transforma- tion (CCT) procedure developed previously, aiming at emulating the typical condi- tions encountered in polymer processing. Several samples characterized by a homoge- neous structure were solidified from the melt at various cooling rates and the result- ing structure and properties were subsequently evaluated by analyzing the density, microhardness (MH), and wide angle x-ray diffraction (WAXD). The resulting solidifi- cation behavior was then compared to that exhibited by the individual constituents of the blend (i.e., PBT and PET). The blend displayed a unique solidification behav- ior, conversely to those of the pure components which showed characteristics not rec- ognized in the blend except at certain restricted cooling rates ranges. The cooling rate dependence observed in the blend does not bring similarities to the crystalliza- tion behavior of individual constituents since the fall down of density with cooling rate should be related to the rate controlling demixing stage of the two moieties just before crystallization occurs. The kinetics observed is thus a measure of the kinetics of demixing