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

Abstract

AbstractPoly(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). 2θ 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. J Appl Polym Sci 104: 137–146, 2007