Sample fibers were prepared with a multi-filament melt-spinning machine, from polypropylene (hereafter "PP") to which beta-form nucleating agent had been added. The relations between melt-spinning conditions and crystal modification of obtained fibers were studied. Wide-angle X-ray diffraction measurement of fibers yielded the following results: The diffraction peaks of alpha-form crystal were clearly observed in undrawn fiber to which beta-form nucleating agent had been added in an amount of 0.05 wt. The diffraction peaks of beta-form crystal were observed in undrawn fiber to which beta-form nucleating agent had been added in an amount of more than 0.10wt. Also, the effects of spinning temperature on PP to which beta-form nucleating agent had been added in an amount of 0.10 wt were studied. Only crystalline reflections of alpha-form were found in the sample produced at a spinning temperature lower than 250 deg C. However, the reflections of beta -form appeared when spinning temperature was increased to 280 deg C. When the draft ratio was more than 3100, the diffraction peaks of beta -form crystal were found when the draw ratio was set at 4.0, but the peaks were never found when the draw ratio exceeded 5.0. The results indicate that crystal transformation from beta -form to alpha -form takes place in samples for which the crystallite-orientation factor of beta-form, f_C(beta), reaches about 0.788.
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