AbstractAn experimental study was carried out to investigate the influence of molecular weight distribution on stretchability and thread nonuniformity of high‐density polyethylene monofilaments. For the study, a melt‐spinning/multistage stretching device was constructed, and the monofilaments were extruded first into a quench tank and subsequently stretched twice in an annealing bath. Processing variables investigated were (a) the extrusion temperature, (b) the shear rate in the spinnerette hole, (c) the air‐gap distance, (d) the annealing bath temperature, (e) the take‐up speed at the first‐stage stretching, and (f) the take‐up speed at the second‐stage stretching. Fiber samples were collected at each stage of stretching, namely, (a) as melt‐spun, (b) after the first‐stage stretching, and (c) after the second‐stage stretching. The maximum stretch rate at which thread breakage occurs was determined at the first‐and second‐stage stretching in the annealing bath. The melt‐spun materials were three different grades of Mitsui Petrochemicals high‐density polyethylene and two different grades of Union Carbide high‐density polyethylene. Also melt spun were blends of two Mitsui polyethylenes and the two Union Carbide polyethylenes. An attempt was made (a) to correlate stretchability with the molecular weight distribution of the high‐density polyethylene; (b) to identify the influence of spinning conditions on stretchability for a given polymer; (c) to correlate the variations of the fiber diameter with the molecular weight distribution and spinning conditions, and (d) to correlate the stretchability of a blend system with blending ratio. tensile properties (the tensile strength at the yield point, tensile elastic modulus, and percent elongation at break) were determined for all fiber samples collected, using the Instron tensile tester. For some fiber samples of special interest, selected on the basis of the spinning experiment results, wide‐angle x‐ray diffraction measurements were taken to determine the
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