A THEORETICAL AND EXPERIMENTAL STUDY OF CRYSTALLINE/COMPATIBLE POLYMER BLENDS

The crystallinity and melting of compatible poly((epsilon)-caprolactone)/poly(styrene-co-acrylonitrile) (PCL/SAN) blends were monitored for samples prepared from both the melt and solution. The development of PCL crystallinity was observed to be dependent on both the blend composition and preparation technique. The glass transition temperature was observed to be a primary cause of the compositional dependence of crystallinity. Solution-casting was found to be a technique capable of increasing crystallinity levels for some compositions. The melting behavior of the blends was rather complex. Solution-cast samples exhibited a single endotherm which decreased in temperature with increasing SAN concentration. Both thermodynamic and morphological effects are cited as possible causes of this behavior. Melt-crystallized samples exhibited dual melting endotherms whose magnitudes vary with blend composition. The melting point of the lower temperature endotherm increased with increasing SAN concentration. A mechanism based on melting, recrystallization, and subsequent remelting was invoked to explain the behavior of the melt-blended specimens.;The determination of polymer/polymer interaction parameters ((chi)) from melting point data is critically reviewed with emphasis on two major areas. The first concerns variations of morphology with blend composition which can restrict attempts to calculate (chi) if non-equilibrium melting points are used. An equation is presented which relates the experimentally observed melting point depression upon blending to the thermodynamic melting point depression and a morphological term which accounts for changes in lamellar thickness. Other morphological factors such as crystalline perfection and size are discussed. The second area of interest involves processes such as lamellar thickening during thermal analysis which can seriously impair determination of "true" crystalline melting points. Finally, methods for directly determining blend equilibrium melting points are discussed.;The spherulitic superstructure and mechanical properties of SAN/PCL blends were also monitored for samples prepared from both the melt and solution. The mechanical response was related to the blend glass transition temperature and the level of crystallinity. The PCL crystalline superstructure was observed to decrease in size and become more irregular upon the addition of SAN for both sample preparation schemes.