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 (A FM). The surface structures are correlated to x-ray diffraction, birefringe nce, and fiber tenacity. The surface morphology of as-spun fibers is spheru litic at spin draw ratios lower than 500. With increasing spin draw ratio, the morphologies develop into epitaxially crystallized structures, and a sh ish-kebab morphology is evident with spin draw ratios higher than 1000. Whe n tow drawing is applied to spherulitic as-spun fibers, the surface morphol ogy 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 1 2.3 nm. The difference between the long period values determined by AFM and SAXS is 2% on average, indicating that the lamellae spacing between the su rface and the bulk of the fibers is almost equal. Discontinuities in the lo ng period as a function of spin and tow draw ratios are assigned to the mor phological transformations revealed by AFM.