Porous poly(vinylidene fluoride) membranes were graft modified with acrylic acid by radiation-induced grafting utilizing electron beam. When the grafted membranes were characterized by the measurements of convective permeability, diffusion, and ion exchange properties, the membranes showed properties of variable permeability membranes with respect to the permeability of solvent and the ionic semipermeability. The permeability for the studied membranes (extent of grafting varied from 0 to 93 wt %) can be controlled by the ionic strength and pH of the permeate. The more grafted the membranes are the greater are the changes in the permeability; e.g., for the extent of grafting of 85 wt % the permeability increases ca. 4 orders of magnitude when the electrolyte concentration is increased from 10 mM to 1 M. The membranes with the extent of grafting of ca. 10 wt % or more appeared to have equal charge density on the pore walls resulting in the same cation transference number.

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.

On-line corona treatment of polypropylene (PP) fibers during melt-spinning is studied. After extrusion of pp filaments, collected fiber tow is subjected to corona treatment prior to drawing, crimping, and cutting into staple fibers, and wettability, antistatic, and friction properties of treated fibers are characterized. Corona treatment results in an average decrease of 5-10° in the advancing contact angle and of 10-25° in the receding contact angle for water on fibers. With amounts of spin finish lower than 0.2% by weight of fiber, treated fibers have considerably better antistatic properties than untreated fibers. Treated fibers have an order of magnitude lower electrical resistance and about 50% less static charge build-up during carding than untreated fibers. In addition, there is a sharp change in wetting and friction properties of fibers with corona treatment when the amount of spin finish is between 0.12 and 0.13 wt %. These effects are attributed to improved wetting of the treated fibers by spin finishes, leading to a more uniform spreading of finish agents on the fiber surface.

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.