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

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^-1). 26 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, strain-induced 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 200°C further increased the crystallinity of the drawn extrudates but had little effect on the texture. © 2007 Wiley Periodicals, Inc.