Morphology and adhesion force of Aramid fibrids

Aramid pulps (or fibrids) often act as binder in aramid sheet, its features of morphology and binding properties are very important for the mechanical, dielectrical and thermal properties of aramid sheet. The microstructure features of aramid pulps were characterized by atomic force microscopy (AFM) in tapping mode, as well as the scanning electric microscopy (SEM) and polarized optical microscopy (POM). The binding properties of pulps, were determined by adhesion force with AFM tip coating technique. The aramid pulps exhibit ribbon-like shape in SEM, branching crystal in POM, and grain like in AFM, which indicated the high shearing forces in its producing process. It can be made into sheet, and the surface features had greatly changed after the fibrids sheet was calendered at high temperature and pressure. They were adhered together and the bonding strength significantly increased. The surface of fibrids sheet became smoother after calendering. The adhesion forces between the fibrids, were measured by AFM pull-off force. AFM force-distance curves, between grafted tips and screened fibrids surface, were carried out in contact mode. Calibration of the cantilever (spring constant and tip radius) is of major importance to obtain quantitative data. The tip was coated with fibrids. and then the fibrids-fiber force, and fibrids-fibrids force was measured.