Huihui Li, Shujing Zhang and Shouke Yan
Beijing University of Chemical Technology, Beijing, China
For partially miscible crystalline/amorphous polymer blends, the combined effects of phase separation and crystallization can result in multiple morphology. In this study, the effects of composition and melting time on the morphology and structures of poly(propylene carbonate)/poly(3-hydroxybutyrate) blend thin films was investigated. A low PPC content in the film resulted in compact PHB spherulites, filling the whole space, whereas the amorphous PPC spherical microdomains scatter in the PHB region. With increasing PPC component and melting time, a large amount of PPC aggregates to the surface to form a network uplayer, whereas the PHB thick domains connected by its thin layer form a continuous PHB region, leading to a superimposed bilayer structure. If PPC content reached 70 wt%, a PPC-top and microporous PHB-bottom bilayer structure can be developed. We suggested that phase separation can take place mainly along the normal direction of the film surface at 190 ºC, attributed to the different surface energies of the two components. After cooling, the crystallization occurred, leading to further segregation and solidification along film planes. This superimposed bilayer by interplay between phase separation and crystallization may provide availability to tailor the final structure and properties of crystalline/amorphous polymer films.