Single and double bubble tubular film extrusion of polyethylene 2, 6‐naphthalate (PEN)

An experimental study of film formation and structure development of polyethylene 2,6‐naphthalate (PEN) in single and double bubble tubular film extrusion is presented. PEN was largely stable in film blowing. The films produced were characterized with wide angle X‐ray diffraction, DSC, and Abbe refractometer techniques. The structure and orientation in the films varied substantially with process and film formation history. Single bubbles exhibited polymorphs with considerable levels of orientation, while double bubbles possessed only the extended α‐modification. With increasing planar strain, the naphthyl rings on the chain backbone became increasingly aligned parallel to the film surface. The mechanism of structure evolution in PEN was related to its behavior during the inflation period and compared with that found in polybutylene terephthalate (PBT) and polyethylene terephthalate (PET).