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

Abstract

A (20/80) blend of poly(ethylene 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 extrudates 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.

Effect of orientation on the free volume and oxygen transport of a polypropylene copolymer

“…Stretching EP4.5 films under the constrained uniaxial conditions used in this study resulted in neck formation and propagation, followed by uniform strain hardening. The natural draw ratio value of EP4.5 was about 5.5, similar to that of polypropylene 17. Uniformly oriented films were obtained through stretching to various λ values in the strain‐hardening region.…”

Poly(ethylene terephthalate)/polypropylene microfibrillar composites. III. Structural development of poly(ethylene terephthalate) microfibers

“…Obviously, the transition was a result of molecular relaxation. Attempts were made to study the texture of the PET microfibers; unfortunately, they became randomly oriented after xylene extraction,2 and pole figure analysis was not possible.…”

“…The extrudate was immediately quenched in a water channel after the die. The details of the solid‐state drawing process have been reported earlier 2. The distance between the clamps was 10 mm; therefore, the corresponding draw rate was 0.0167 s −1 for the minimum draw speed of 10 mm/min and 1.67 s −1 for the maximum draw speed of 1000 mm/min used in this study.…”

“…The crystallinity of the PET samples before and after solid‐state drawing and after annealing was determined by DSC. The details have been reported earlier 2. The enthalpy of melting of crystalline PET was taken to be 140 J/g 10…”

“…In previous articles,1, 2 the morphological development of a 20/80 blend of poly(ethylene terephthalate) (PET) and polypropylene (PP) in melt extrusion and its solid‐state drawing behavior are reported. Strain‐induced crystallization of PET occurs, and its extent is a parameter of the drawing condition and draw ratio 3, 4.…”