Evaluation of Inter-fiber Bonding in Wood Pulp Fibers by Chemical Force Microscopy

Atomic force microscopy with chemically modified tips was used to evaluate the inter fiber bonding properties of typical wood pulp fibers. Using –OH functionalized AFM tips as a model of cellulosic pulp fiber surfaces, pull-off forces and work of adhesion were measured in aqueous media. Three distinct tip-surface interactions were identified from force-displacement curves, representing three typical surface conditions of wet pulp fiber surfaces: solid, swollen and micro-fibrillated. The work of adhesion calculated shows that van der Waals forces are the major contributing factor on non-swollen solid regions of fiber surfaces. The difference in inter-molecular bond strength of different pulp fibers is relatively small. The inter-fiber bonding properties of pulp fibers are mainly controlled by the surface deformability, which determines the area of molecular contact at fiber-fiber physical interaction points.