Double bubble tubular film extrusion of polybutylene terephthalate-polyethylene terephthalate blends

A technology has been developed to produce biaxially oriented films of blen ds of polybutylene terephthalate (PBT) and polyethylene terephthalate (PET) using double bubble tubular film extrusion. The mechanical instabilities a nd the mechanisms associated with their sources of occurrence are described . Bubble stability varies substantially with deformation and composition. T he Rims have been structurally characterized with wide angle X-ray diffract ion and optical techniques. The individual phases in the blends oriented di fferently. We have proposed a model of crystalline morphology in biaxially oriented PBT/PET blend films. The structure of the film is related to proce ssing conditions.