Surface Morphologies of Polypropylene Fibers Studied by Atomic Force Microscopy

Surface morphologies of compact-spun polypropylene fibers spun with varying spin and tow draw ratios are characterized with atomic force microscopy (AFM). The surface structures are correlated to x-ray diffraction, birefringence, and fiber tenacity: The surface morphology of as-spun fibers is spherulitic at spin draw ratios lower than 500. With increasing spin draw ratio, the morphologies develop into epitaxially crystallized struc tures, and a shish-kebab morphology is evident with spin draw ratios higher than 1000. When tow drawing is applied to spherulitic as-spun fibers, the surface morphology transforms into a fibrillar structure between draw ratios of 2.0 and 3.0. With the highest applicable draw ratio of 4.4, the microfibrils consist of alternating crystal blocks and amorphous regions with a periodicity of 12.3 nm. The difference between the long period values determined by AFM and SAXS is 2% on average, indicating that the lamellae spacing between the surface and the bulk of the fibers is almost equal. Discontinuities in the long period as a function of spin and tow draw ratios are assigned to the morphological transformations revealed by AFM.