Surface morphology of melt-spun polypropylene (PP) filaments, spun from an additive-free PP powder and from a commercial-grade PP with different draw ratios, were examined with atomic force microscopy (AFM). The surface morphology of as-spun filaments was spherulitic. The gradual transformation of the surface structure from a spherulitic morphology to a fibrillar morphology during stretching was studied. In the filaments spun from the commercial-grade PP, the transformation was initiated by deformation of spherulites with a draw ratio of 1.2 and continued with association of lamellar stacks into fibrillar chains with a draw ratio between 1.2 and 2.0. A hierarchical morphological microstructure of fibrils, microfibrils, and nanofibrils was developed with a draw ratio of 4.0. In the filaments spun from the additive-free PP, the association of lamellar stacks into fibrillar morphology occurred considerably later, between draw ratios of 2.0 and 4.0. An oriented lamellar structure was found in these filaments, still with a draw ratio of 4.0.

For a better understanding of the structure, distribution, and composition of spin finish layers on fiber surfaces, scanning force microscopy techniques are used to image spin finish layers on polypropylene fiber surfaces with submicrometer resolution. The polypropylene staple fibers are made into nonwovens, and common antistatic, wetting, and hydrophobizing agents are the spin finishes. Distribution and thickness profiles of the wax-like antistatic and hydrophobizing agents are successfully measured with con tact mode atomic force microscopy and lateral force microscopy. Nanometer scale measurements of local adhesion forces and elastic moduli of the spin finish layer sur faces by force modulation techniques (pulsed force mode) provide further information on the distribution and composition of the spin finish layers. In addition, the oil-like wetting agent layer, which is too soft and sticky for contact mode measurements, can be imaged with the pulsed force mode technique.

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