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.

Poly(ethylene terephthalate) was extruded, solid-state-drawn, and annealed to simulate the structure of poly(ethylene terephthalate) microfibers in a poly(ethylene terephthalate)/polypropylene blend. Differential scanning calorimetry and wide-angle X-ray scattering analyses were conducted to study the structural development of the poly(ethylene terephthalate) extrudates at different processing stages. The as-extruded extrudate had a low crystallinity ($ 10%) and a generally random texture. After cold drawing, the extrudate exhibited a strong molecular alignment along the drawing direction, and there was a crystallinity gain of about 25% that was generally independent of the strain rates used (0.0167-1.67 s À1 ). 2y scans showed that the strain-induced crystals were less distinctive than those from melt crystallization. During drawing above the glass-transition temperature, the structural development was more dependent on the strain rate. At low strain rates, the extrudate was in a state of flow drawing. The resultant crystallinity hardly changed, and the texture remained generally random. At high strain rates, straininduced crystallization occurred, and the crystallinity gain was similar to that in cold drawing. Thermally agitated short-range diffusion of the oriented crystalline molecules was possible, and the resultant crystal structure became more comparable to that from melt crystallization. Annealing around 2008C further increased the crystallinity of the drawn extrudates but had little effect on the texture.

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