Abstract
A high-resolution Raman mapping method has been developed in order to obtain 2D information about structural anisotropies (crystallinity, molecular alignment) in thin filament cross-sections (diameters between 27 μm and 79 μm). Cross-sections of melt-spun, hot-drawn poly (ethylene terephthalate) (PET) filaments and bicomponent core-sheath PET-polyamide 6 (PA6) filaments have been scanned through a laser beam (spatial resolution <1 μm). Raman spectra were analyzed with a specifically developed peak fitting method to obtain Raman maps, e.g., mapped peak height ratios across the face of the fibers. These maps reveal microscopic interconnected networks of crystalline strands within a low crystalline matrix. Radial gradients in PET crystallinity, as well as average and surface crystallinities, were determined. The presented Raman mapping method to visualize variations in the PET crystallinity across such fine filament cross-sections, and the findings thereof, open a new pathway to better understand how fiber processing parameters affect radial fiber structures.
Highlights
Among synthetic fibers, poly (PET) fibers have the highest production volume worldwide and are widely used in sectors like automotive, furnishing, homewear, sportswear, technical wear amongst other sectors [1]
Structural studies on fibers focus on comparing average quantities like crystallinity, molecular orientation, long-spacing or crystallite sizes, extracted from e.g. wide-angle x-ray diffraction (WAXD) or small-angle x-ray scattering (SAXS) patterns [4,5,6,7]
Calculated average crystallinity values from Raman mapping of entire fiber cross-sections are summarized in Table 6 and are compared to values obtained by other methods (DSC, WAXD [23])
Summary
Poly (ethylene terephthalate) (PET) fibers have the highest production volume worldwide and are widely used in sectors like automotive, furnishing, homewear, sportswear, technical wear amongst other sectors [1]. Structural studies on fibers focus on comparing average quantities like crystallinity, molecular orientation, long-spacing or crystallite sizes, extracted from e.g. wide-angle x-ray diffraction (WAXD) or small-angle x-ray scattering (SAXS) patterns [4,5,6,7]. Of particular interest for technical textiles is the detailed microscopic 2D structure (crystallinity, molecular alignment) of poly mer fiber cross-sections, since it strongly influences the mechanical properties and affects the surface characteristics of the fibers. Radial gradients in, e.g., molecular orientation or crystallinity can strongly affect the abrasion resistance of polymer fibers [8]. It is, very challenging to obtain 2D structural information across polymer filament cross-sections with diameters below e.g. 80 μm. Results thereof are shown in the data in brief [23]
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