Raman spectroscopy for spinline crystallinity measurements. I. Experimental studies

Online Raman spectra, obtained at different points along the spinline during the melt spinning of polypropylene homopolymer (hPP) fibers, are presented. The percentage crystallinity corresponding to each spectrum was determined from the normalized intensity of the 809-cm−1 Raman band. A calibration curve for propylene crystallinity was established offline with compression-molded films and fibers spun under different processing conditions. Several hPPs and propylene–ethylene copolymers (with 5–15% ethylene) were used to cover a wide calibration range for propylene crystallinity (9.5–60.9%) with an R2 value of 0.989. This calibration curve was subsequently used to predict the polypropylene crystallinity in the spinline as a function of distance from the spinneret. Under identical conditions of quench and throughput, at a fixed point along the spinline, the overall crystallinity developed in the fiber was found to increase with an increase in the spinning speed. As the spinning speed increased, the point of the onset of crystallization moved closer to the spinneret. The rise in crystallinity was more gradual, at 750 m/min as opposed to 1500 m/min. Increasing the throughput at constant spinning speed was found to decrease the rate of crystallization because of a decrease in the spinline stress. At a fixed distance from the spinneret under identical conditions of quench and spinning speed, fibers spun at a higher throughput showed less overall crystallinity. The onset and rate of crystallization was found to be faster in the lower melt index H502-25RG resin as compared to the 5D49 resin under the spinning conditions explored. The experimental data presented here were used to validate fundamental fiber-spinning models (see part II of this series of articles). The validated models and experimental observations can be used to guide the fiber spinning of isotactic polypropylene for rapid product development. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008