Frictional properties of fiber assemblies from different cotton varieties were investigated using a sliding friction tester. Results indicated that frictional characteristics of cotton fibers varied significantly among varieties. A significant, negative correlation between friction coefficient (u) and fiber yellowness and a strong positive correlation between u and short-fiber content were observed. Multilinear regression analysis showed that fiber friction is a complex phenomenon that depends on fiber dimensional, mechanical, and surface properties. In addition, a fiber simulation model was developed to explain the partial relationships between the fiber dimensional properties and its frictional characteristics. The model shows that, for assemblies of fibers with the same mass and equal average mean length, the true contact area increases with decreasing fiber maturity and fineness. In the second phase of this research, surface of cotton fibers from two different samples--with statistically distinct macroscale frictional properties--were further characterized at the nanoscale using various atomic force microscope (AFM) operation modes. A cotton fiber surface is naturally coated with a few hundred nanometer-thick layer of lipids, fatty acids, alcohols, and pectins, collectively called the cotton cuticular wax. Surface topography and friction images of the fibers were obtained with conventional contact mode AFM. The nanomechanical property images--such as adhesion and deformation--were obtained in force tapping mode. The results indicate that fibers with higher macroscale friction were also associated with higher nanoscale friction, adhesion, and deformation. The differences in nanoscale friction, adhesion, and deformation signals is attributed to fiber surface hydrophobicity and stiffness, which in turn may depend on the waxy layer thickness, fatty acids hydrocarbon chain length, and film viscosity.
