Study on poly(ethylene terephthalate)/polypropylene microfibrillar composites. II. Solid-state drawing behavior

Abstract

A (20/80) blend of polyethylene terephthalate)/polypropylene (PET/PP) was solid-state drawn to enhance the molecular orientation of the PET microfibers. Effects of drawing temperature (23-140°C) and drawing speed (max. 1000 mm/min) on the morphology and draw ratio of the blend were studied and discussed based on the drawing behaviors of the pure polymers. In cold drawing, there seemed to be a critical drawing speed below which the natural draw ratios of the polymers remained constant, but above which the draw ratios first decreased slightly because of suppression of molecular relaxation and then increased because of breakage of highly strained molecules and disintegration of lamellar crystals into finer mosaic blocks. Macroscopically, the pure PP and the PET/PP composite extru-dates gave similar draw ratios at the same speeds. SEM showed that the PET microfibers suffered a smaller elongation than the PP matrix and severe voiding occurred at the PET/PP interface. Furthermore, substantial fiber breakage occurred during cold drawing at speeds above 200 mm/ min. In comparison, drawing at 100°C caused no obvious interfacial voiding and fiber breakage. Furthermore, the natural draw ratio of the blend was lower than that of the pure PP extrudate, indicating that the PET microfibers had constrained the deformation of the PP matrix. © 2004 Wiley Periodicals, Inc.