Processing-structure-properties relationship of multilayer films. 1. Structure characterization

Low density polyethylene (LDPE)/poly(ethylene terephthalate) (PET) multilay er films with and without a reactive tie layer were prepared by blowing pro cess. The layers contents were fixed and the parameters evaluated were blow -up ratio (BUR), draw-down ratio (DDR) and frost-line height (FL). Their ef fect on the structure was studied. No crystallinity for the PET layer was i nduced by the blowing process. The orientation of the multilayer films was characterized by birefringence and infrared spectroscopy (FTIR). The measur ed birefringence showed a negligible orientation for PET layer, and the LDP E layer oriented mainly along the machine direction. FTIR characterization also showed a negligible orientation for PET layer, and for LDPE layer, the crystalline a-axis tended toward machine direction, crystalline b-axis loc ated in transverse-normal plane with no orientation for the amorphous phase . The lamellar arrangement of LDPE layer with respect to machine direction was obtained by dissolving the amorphous phase in solution of potassium per manganate in a mixture of equal volumes of orthophosphoric and sulfuric aci d. The crystallization of oriented LDPE melts produced a morphology consist ing of rows of lamellar crystals aligned parallel to the machine direction at higher draw-down ratio. It was not always of the row-nucleated type, the exact morphology patterns greatly depended on the distribution of the crys talline a-axis and b-axis orientation, which in turn was dependent on DDR, BUR and frost-line height. (C) 2001 Elsevier Science Ltd. All rights reserv ed.