Friction hysteresis of paper

he purpose of this investigation was to characterize the dependence of paper-to-paper friction on the sliding direction of the previous slide for various paper grades. Static and kinetic friction forces and coefficients of friction were measured using a friction tester based on the horizontal plane principle. The papers were also characterized with respect to fiber-rising tendency and they were imaged by environmental scanning electron microscopy (ESEM). The results showed that uncoated papers exhibited a behavior where the coefficient of friction rapidly decreased to a low value with repeated slides over the same track in the same direction. When the sliding direction was reversed the coefficient of friction increased and maintained a high level. A term called friction hysteresis is defined to quantify these effects in order to relate the behavior of the coefficient of friction to various characteristics of the paper. ESEM imaging showed that sliding caused fiber ends to rise out of the plane of the paper surface and to align themselves in the sliding direction. A correlation was found between the magnitude of friction hysteresis of the different papers and the total area of the raised fibers. The results suggest that friction hysteresis is due to the interlocking of fiber ends on the paper surfaces and that the degree of interlocking is influenced by the orientation of fiber ends relative to the sliding direction.