AbstractData are presented which characterize the behavior of fibers produced from polypropylene polymers under experimental conditions designed to investigate the effect of extrusion temperature on various properties. At high extrusion temperatures molecular weight degradation takes place which results in a lowering of the average molecular weight and a narrowing of the molecular weight distribution. The orientation and crystallinity characteristics of the undrawn fibers also vary with extrusion temperature. The crystal structure of the fibers shows a gradual transformation from a highly ordered monoclinic crystal structure to paracrystalline structure of lower orientation as the extrusion temperature is increased. Drawing of the undrawn fibers of various molecular weights has been characterized by dynamic stress‐strain curves and followed by sonic velocity measurements, the results of which suggest in agreement with other methods that the reduction in crystallinity during drawing is a function of the undrawn crystal structure, the drawing rate, and the drawing temperature. Drawn fibers produced from 21 isotactic polymers have been compared for tensile strength behavior by selecting fibers at the same average molecular weight but with different molecular weight distributions and also with similar molecular weight distributions but at different average molecular weights. These comparisons have shown that at a common draw ratio the tensile strengths of the fibers are lower for those fibers with broad molecular weight distributions when compared to fibers with narrow molecular weight distributions at same average molecular weight. The data also show that the tensile strengths of the fibers of the same molecular weight distribution and crystal structure increase with increased average molecular weigh
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